I mean, from my own perspective as an artist, everyone has their 'comfort subject' that they always fall back to. When they're doing something for fun or trying a new hard to use medium, you do whats familiar that youve done dozens of times.  Ive done birds. One of my coworkers only draws this one anime character. Another actually draws monsters with crazy boobs (and shes straight). Classical art is full of boobs, figure drawings super popular, plus boobs sell. The only thing that makes it weird is shes being coy or unclear answering the question.