But how could a seed AI be able to make itself superhuman powerful if it did not care about avoiding mistakes such as autocoreccting "meditating" to "masturbating"?

Those are only 'mistakes' if you value human intentions. A grammatical error is only an error because we value the specific rules of grammar we do; it's not the same sort of thing as a false belief (though it may stem from, or result in, false beliefs).

A machine programmed to terminally value the outputs of a modern-day autocorrect will never self-modify to improve on that algorithm or its outputs (because that would violate its terminal values). The fact that this seems silly to a human doesn't provide any causal mechanism for the AI to change its core preferences. Have we successfully coded the AI not to do things that humans find silly, and to prize un-silliness before all other things? If not, then where will that value come from?

A belief can be factually wrong. A non-representational behavior (or dynamic) is never factually right or wrong, only normatively right or wrong. (And that normative wrongness only constrains what actually occurs to the extent the norm is one a sufficiently powerful agent in the vicinity actually holds.)

Maybe that distinction is the one that's missing. You're assuming that an AI will be capable of optimizing for true beliefs if and only if it is also optimizing for possessing human norms. But, by the is/ought distinction, there is no true beliefs about the physical world that will spontaneously force a being that believes it to become more virtuous, if it didn't already have a relevant seed of virtue within itself.