wow the author is a guy, and his style is pretty femenine

female, not male: https://www.mangaupdates.com/authors.html?id=1288

You said that bc she draw herself as a man, right?
Maybe she is a man, or maybe she likes others think about her like a man.
This is so confusing. （￣へ￣）

maybe sensei just using men's pen name like Hiromu Arakawa sensei (but she is real female) (=・ω・=)

Or maybe they're gender fluid and it really doesn't matter what sex they are.

Or maybe it's just that it seems to be pretty common for mangakas of BL to use male pen names.

In Japanese society in general, and in the manga industry in particular, women are not highly regarded or seen as capable as men. I know it isn't fair, but that is just how it is. Thus, women in the manga industry, and particularly the BL/yaoi genre, tend to take male, or androgynous, pen names to avoid being dismissed out of hand simply for being female. It is also an excellent way to maintain anonymity. No one would expect someone with a masculine name to be a woman.