Yeah...this should probably be tagged trans(which doesn't currently exist) rather than yaoi based on the current trajectory. This seems like a totally het couple(though one is still an egg).
Assuming that someone considers themselves a girl just because they like cute and fluffy stuff and want to be a princess is a bit presumptuous. Wanting a bunch of things that are associated with a certain gender is not the same as wanting to be that gender for everyone.
If it was just that "they like cute and fluffy stuff", I wouldn't have made such an assumption. The person associates themselves with the labels of "girl" and "princess". I don't think it's too presumptuous to assume someone that considers themselves this way would want to be seen this way. This isn't a person wanting to be a prince that wears skirts and likes cute and fluffy things. This is a person wanting to be a princess. There is a substantial difference.
As an aside, I haven't finished reading the two chapters after this one, yet; it's possible I will encounter something that will change my mind, but in the meantime:
For me, this is pretty hard-line-in-the-sand stuff: While the phrase "I want to be a princess" is a classic element of the narratives of trans women, you definitely don't get to go around deciding for people what their gender is based on a few things they said (unless one of those things was "I am a [girl/boy/other]", or something similarly unambiguous).
Doubly so if "I wanna be a princess" was said while sopping drunk, as in this chapter—but even without that, it could still in this context mean, for instance, "I want to wear dresses and have a prince on a white horse who will bring me flowers and protect me and treat me like I'm the most special thing in the world," without necessarily meaning, "I think I'm really a girl inside".
So far, he's been saying, "I am a gay man." If he weren't a fictional character, and we were good friends with him (or just pushy I guess), we could perhaps ask him how he felt about the matter, but we can't. In the meantime, he identifies as a man and it would be quite rude to identify him as a woman on the assumption that he just doesn't understand himself yet.
It does kinda feel like he's trans and being unaware of it himself, not because of his feminine personality but mainly because he said "but then my body started to bulk up so I realized I was a man after all". It's like he didn't fully realize that his body was of a man. It was quite similar for me when I first experienced dysphoria. I'm not saying he's definitely trans but there's a slight feeling that he might be.
But even if he's not that's still totally fine. Men should be allowed to love cute things too.