1. Goku knows exactly how many seconds are there before Cell explodes, yet ends up staying around and talking, even when Cell directly says "4 seconds left" Goku still takes his sweet time. The author wouldn't draw Goku casually talking to Kaio with his fingers off his forehead if it was meant to be seen as instantenous.
2. Goku's apology to ChiChi, Goku having no genuine remorse for anything he does is one of his most defining traits, soon after his death when Kaio blames Goku for killing him, Goku's reaction is "I apologized, didn't I? Why can't you let go of it?" so if you take Toei's interpretation of Goku apologizing for always being selfish it's like he suddenly developed conscience and then immediately dropped it. It's more likely that Goku apologized for abandoning ChiChi preemptively showing premeditation.
3. You may say that Goku wouldn't know about strong martial artists of the past yet - this plot point seems to have been planned in advance with a hidden dialogue, Kaio's remark is very similar to what Goku uses as his excuse on the lookout later.
"I guess I couldn’t quite get them to grasp the elements of “poison” that slip in and out of sight among the shadows."
"Also, this is often misunderstood, but I’m not good with wholesome content. It may seem wholesome at first glance, but there’s actually poison inside."
Your thoughts? Note that Goku's "I'm proud of you." that adds warmth to the scene is Viz' mistranslation, in the original version it's "I was very impressed.".