
Actually, it's not. That's the stereotypes they're trying to get rid of in this manga. And there is a reason Kiyomi acts the way she does. I think it's actually pretty obvious from the first chapter...?

I think what they mean is that this particular trait, e.g sewing, would make people describe Asuka as girly, stereotyping it as something girls and only girls do. This manga does try to break the whole stereotype by switching roles, and I personally don’t find this manga that sexist, but I get where OP is coming from.
I couldn't read more than one chapter because this is way too sexist for me.