Galettes are not pancakes! Don't believe rumors saying otherwise, you can see what they look like yourself with a quick google search. In this case, Petit Galette is a booklet released alongside the larger Galette anthology, which itself is the second-longest-running yuri anthology of all time and is the only consistently running magazine other than Yuri Hime.
So this one isn't random at all. As for the larger publication, I think they just wanted a name that screamed "Yuri~!" and wasn't a macaron. Since galettes are a sort of high-class cafe dessert offering, at least around these parts. Stylish, hip, modern.
