This is a very tired insult/joke outsiders throw around about vtubing (though I don't get the impression that you had that intention). It's somewhat ridiculous, vtubers stream very often and voice changers tend to be pretty obvious. There are some men who use female avatars, but it isn't common.
It's also kinda misogynistic, plenty of women enjoy anime culture. Many prominent artists for vtuber models are also women (and occasionally vtubers themselves). To the level that calling the model artist "mama" and the model rigger "papa" is a common trope.
Hentai porn is apparently the most popular porn category in lots of countries! Took me by surprise when I found that out. Closely followed by the more predictable “lesbian”, “Anal”, “MILF” and “Asian”!