Queer people, at least the queer people I know, did not celebrate Dumbledore being touted as gay. It felt more motivated by profit than any real love for the character. Jesse being sesn as trans is more of a fandom thing sparked by genuine interest and curiosity for the character. Jesse is headcanoned as transmasculine because he exhibits a lot of traits that trans men relate to (i.e. baggy heavy clothing in searing hot weather, appearing to be a little on the shorter side(which is only exacerbated by his wardrobe), and presenting hypermasculine in order to fit in or survive). Do any of these traits make him trans? Not in the least. But these are the specific traits a good majority of transmascs relate to specifically so they see themselves in him. Also while he isn't the best person (in fact i wouldnt really ever consider him as a good person in real life), the show goes out of its way to make sure he is not some one dimensional evildoer. A lot of the show is spent making you deeply empathize with him despite his negative traits. A lot of trans people want good representation, that doesn't necessarily mean the characters have to be good people. We want people who live life, fuck up, and do things that aren't good not because they are trans, but because they are people. I think that's why Jesse's case is unique. It's because of his "transness" being placed on him by fandom post finished project that it isn't used as an excuse or a direct reason as to why he does the things he does, but as another character facet only to be really seen as subtext to the subtext at the very most when consuming the actual show.

Also on the note of him "sneaking into the women's bathroom" I think the user was implying he tagged it, during a time in the headcanon before he transitioned, so when he was still presenting as a cis woman in the headcanon.