Did Toriyama himself ever comment that Krillin was the strongest Earthling?
http://www.kanzenshuu.com/translations/tenkaichi-densetsu-toriyama-koyama-nozawa/ wrote:Speaking of women who fight, there is No. 18.
Toriyama:
Ah, that’s right. No. 18 becomes Kuririn’s wife in the end.
Nozawa:
Ah, I was surprised at that, too! All the voice actors wondered, “Why did she choose Kuririn?” (laughs)
Toriyama:
Kuririn was originally supposed to be just a minor role, so to have him become Goku’s best friend in the blink of an eye…
Koyama:
Well, he is the strongest Earthling male.
Toriyama:
You’re right, he is the strongest among the Earthlings. But in spite of that, he tends to end up in a bad way, so I thought, “once in a while, I have to let him be happy,” and had him get married. (laughs)
Context is important. If it's an in story statement, who says it and to whom does that person say it too.
Yamcha says it to himself.
As for Earthlings, 17 and 18 would be considered Human type Earthlings as both are human (They were modified yes, but born and raised as Human)
True, but their modifications are something that would set them apart from a regular Earthling, Tenshinhan and Krillin don't have anything that set them apart, or would make one consider that Tenshinhan would be excluded from said statement.
Krillin and Tenshinhan are
pure earthlings, no modifications / alien ancestry.
As for the third eye,
(11) What's up with the third eye on my main man Tenshinhan? Is Tenshinhan human?
- Charles Moyer, California; Evan Coltin, Via Internet
Toriyama: "In certain parts of Asia, beings with a third eye on their forehead are thought to be godlike and are said to possess the power of true seeing. It seems that Tenshinhan, who was raised by the evil Tsuru-Sen'nin [Crane Hermit], lost the ability to use the myriad powers of his third eye for good purposes."
Notice how Toriyama doesn't contradict the person and say something like "
No, he's not a human."
Also, the only "being" from Asia that Tenshinhan would most likely be based off of is a human.