This bothers me as well. Using "he" generically is accepted use of the English language so one could be forgiven for continuing to use it. By using "she" you are going out of you way to choose a gender, when you could easily use a gender-neutral pronoun.

Or the person who wrote that might genuinely believe that Satoshi was female.

I don't like reverse-sexism/racism/etc because adding the term "reverse" doesn't stop it from being sexist/racist/etc itself, but Hacker News guidelines say we should "respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith."

Satoshi (さとし, サトシ) is generally a masculine Japanese given name

Using a screen name of the opposite sex is a good way to help hide one's identity. I wouldn't read into it.

Some people don't like using "they" as a singular, myself included, in serious writing.

Though the singular "they" has been in the English language since something like the 14th century, for the past hundred-and-fifty or so years, some prescriptive grammarians have been advising against it, insisting that it's an error. I is perhaps due to the efforts of these grammarians that "they" has come to be regarded as informal, giving text a colloquial or conversational flavor.

How you can avoid sexism is my sometimes using "he" and sometimes "she" as a meta-variable for some unspecified person (consistently for the same person).

If you make the he:she ratio exactly 50% in your corpus, you're above all accusation of sexism.