Certainly no-one would make the claim that "there are (definitely) no aliens in the galaxy" when we can't disprove the idea that aliens traveling at the speed of light just reached the galaxy (with our current understanding of physics). That doesn't mean you can't make the claim "there are (almost definitely) no aliens in the galaxy (because I just created the most amazing telescope ever and looked at every particle of matter in the galaxy and there were no aliens there)". The principle of charity demands that understand the bare claim that "there are no aliens in the galaxy" to mean something that is plausible, such as "there are almost certainly no aliens in the galaxy".
Well, what matters is expectation. The fact that some people win the lottery doesn't prove that playing the lotto is profitable. In fact it isn't money-profitable. The fact that people sometimes win doesn't change the nature of reality, that even for them, the win is unexpected and playing was negative expectation for them.
You seem to be confusing expected value with results.
Do you revise your decision process every time you get unlucky? On a meta level, sure, paying attention to unexpected failures is important to look for systematic errors. But randomly getting unlucky on 99% certainties does not automatically disprove your decision method.
For example, when asked to be more granular, the turtle could say 'I reason that there is only a 1 in 10 chance that seafaring civilizations exist'. The existence of seafaring civilizations doesn't make the turtle wrong in this case.
If the turtle concluded that 'there can not possibly be any seafaring civilizations, because I don't see any' then you could accuse it of bad reasoning.
The hypothetical turtle did exactly that, loyally following suit with the commenter who I replied to.