Both, if she has only sociability, she'll talk to you and other girls, but sexuality adds to that asking for sex from both you and other girls as well. Sexuality by itself would lead to more lewd actions in general, like finding a nice quiet spot to masturbate, but not necessarily asking another person for sex.
Unfortunately, yeah, this is not AA2. It's surprising, given how good it was and still is, that they have not yet gone back to a true Artificial Academy game, but maybe they will after Koikatsu Sunshine.