You do realize it doesn't make a difference what he is, since the point is that he's affiliated with a god? Goku trying to walk under the gravity quite clearly increased his strength. Again, that "Real training" would only take place 'cause Goku would be strong enough to handle the gravity, in which he'd of course need to be stronger. He got stronger by walking under it, thus by that logic running would do the same. Note Piccolo not struggling under it with a battle power of 3,000, note Yamcha not struggling like Goku.Obviously, assistant is different to pet. I mean, where do I start? An assistant is actually a job. He's accustomed to the gravity because he's used to it. As Kaiou's pet, he's presumably been living there for years.
Running does not increase your power. It may improve your leg muscles, but nothing's suggested in the series that it literally rises your strength. Gokuu running under x10 gravity was training because it was him learning to become accustomed to the gravity so Kaiou could put him under the real training, in which they would spar and learn to control ki more efficiently so, hopefully, he'd be able to pull off the Kaiouken and Genki-Dama.
He listens to Kaio like a human would, he communicates with Kaio and Gregory like a human would. So what if he can't speak? Maybe he's unable to? Your "inconsistencies" are entirely subjective. Not to mention you haven't even disputed it, with y'know, your trivial "assistant vs. pet" argument.How do you jump to these conclusions like this? And how do we know that Bubbles is "intelligent", which is entirely subjective and people have different definitions of that word anyway? He can't even speak.
Look, we simply aren't given enough about this type of thing to make definitive conclusions, not to mention the ambuguity/inconsistencies over how gravity corresponds to strength. It's not as cut-and-dry, black-and-white as you think.
By your logic, this man is not an Earthling or human.

Not really, seeing that Bubbles may not have any knowledge of how to use chi. We could just say he's just strong due to the gravity, maybe his battle power mainly attributes to speed, but I've always found there to be a correlation of some sort.Yes, but that 416 has enough power to casually shatter the moon in a Ki blast. It's very hard to believe that monkey is over 5 times that power. You're literally saying as Goku was trying to catch him, Bubbles could have casually turned around, casually and jokingly kneed Goku, and literally put him out of commission several times worse than even Raditz did. Don't you think that's a stretch?
Well, that's all under the assumption that easier is really a concern of mine. I don't look for the easy way out of things, I look for what I believe makes sense to me, so something being easier really doesn't matter to me. If does to you, great, go ahead and take that point of view, but just note that because it's easier, does not make it what everyone would adhere to.That sounds like a lot of factors to keep up with. It's like a buggy Windows 95 with a hundred thousand patches needed and required to make it even relatively stable. Wouldn't it be just easier to you know...think that gravity isn't entirely dependent on power level in the exact way that you're thinking?
Edit:
So it takes Goku 39 days to "get used to the gravity" but it takes him six days to get used to x100? I'm fairely sure it has nothing to do with "getting used to it" so much has it does the battle power of the person.
Bubbles is shown to be Kaio's pet in the "Heavenly Realm", by all means show me how that would not make Bubbles supernatural. He's not dead, so he obviously wasn't from the living world, unless you wanna say Kaio picked him up from a random planet; which causes plot holes in itself. If a human has a battle power of 5 on average, then a little monkey like Bubbles would have even less if he was from the living realm, meaning that he'd instantly be killed by the gravity of Kaio's planet. He's intelligent, being able to understand what Kaio says, which would clearly call for training in that context, unless he's a supernatural monkey and just happens to be naturally intelligent. He also doesn't speak, which like many monkeys, is completely normal. There's plenty of intelligent primate that're able to understand us all to a great level, but Bubbles understands it as if he were human. It's the equivalent to knowing English but being mute or only being able to utter weird noises.
We also don't know if Bubbles is strong, but we know he's fast. It's entirely possible for Bubbles to be stronger than Goku, in fact if you wanna bet technical, he could have easily defeated Goku upon his arrival on the planet. It's considerable that Bubbles knows nothing about chi and therefore can't do anything, but run really fast and or attack with a strength that's in proportion to that speed.
Goku by simply walking around, gets stronger. Look back to when Roshi put a turtle shell on his back, it's the same thing as increasing the gravity, just not as efficient. Goku got stronger, by a long shot from that training.
Goku arriving at Kaio's - 416
-random but plausible gains-
Goku after 10 days - 789
Goku after 20 days - 1,234
Goku after 30 days - 1,678
Goku after 39 days - 1,956-2,123.5
-random but plausible gains-
Bubbles initially on Kaio's planet - 200
After a month - 1,340
After a year - 1,500-2,000
I'd say since all Bubbles really did was walk, run and do aerobic exercises on the planet that once he overcame the gravity, his gains became minuscule and or static, since logically he's used to it. Yamcha is at a battle power of 1,480, he's stated to have struggled to catch Bubbles. Notice how he's able to stand and walk normally, he's just not able to run or exercise like he would on Earth. If Goku at 416 could barley walk, and Yamcha at 1,480, both having never gravity trained before, what does that say? It clearly has to do with battle power, especially since Piccolo at 3,500 and Tenshinhan at 1,830 are shown no signs of struggling. We know they all caught Bubbles between the 18th and 24th, as opposed to Goku's 39 days. This further dictates that the higher the battle power, the easier one can move under gravity until not being affected by it at all.
You could also say that Bubbles is just resilient to the gravity, it really doesn't make a difference by which you go by.