they/them are non-gendered by the older (grammatical) meaning of "gender".

he/his and they/them both have well-established non-gender-specific meanings in the more recent (social) meaning of "gender" (prior to that fairly recent linguistic evolution, words had gender and people had sex -- while its useful to have a term for the distinct feature of people referred to by "gender" as distinct from "sex", its a very different thing than grammatical "gender", and grammatical gender doesn't have a 1:1 mapping to linguistic constructs whose semantics refer to social gender), though he/his also has a gender-specific meaning (and there is considerable potential for ambiguity between the gender-neutral and gender-specific senses of he/his.)