Question about trans people?

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Let me preface this by saying I'm fully 100% in support of all LGBTQ people and I've never had an issue or problem with someone due to their gender or sexuality. I'm a really "You do you, b" person.

Last year, I went to a New Year's party. There was a person there we had never met. They introduced themselves as "Lumis." (In terms of personality, this person was a total pos. They brought their 3 year old child and locked him in his car seat on the kitchen floor the ENTIRE 6 HOUR LONG PARTY, had him in a too-small diaper and refused to change him despite being sopping wet when he asked to be let out and changed, just as brief examples)(yes we said things but they were ignored and it was no one else's place to parent)

Well, they never gave pronouns at first. They were dressed in pretty goth-vibe clothing that was really revealing and accentuated their feminine features. Overall, this person gave very obvious feminine vibes and you really wouldn't expect them to identify as anything other than that, especially with how perverted and over-sexual they were being. Well, I accidentally called them a "she" not really knowing any better. And they FREAKED OUT!! Like, the party totally came to a halt and they started screaming at me, yelling that I misgendered them and their pronouns are "him/he" and if I ever called them a female again they'd do more than just yell at me. I was really taken back by this and super embarrassed so my boyfriend and I left the party immediately. (Found out later that that person eventually got kicked out for being inappropriate after we left)

I also have another friend named Em who I just found out identifies as male, but goes around acting and looking REALLY feminine. He does nothing to imply that he's a male. Like, you really would never know his pronouns unless you asked. He's a WAYY better person than the person we met at the party last year. But I guess my question is, if you identify as a certain gender, why do some people not even try to "pass" as that gender? Like it's not like I have a problem with it and I try to be respectful and not ask and remember their pronouns, but I've always wanted to ask. I totally get surgery is a really expensive thing and not everyone wants or can even afford it, so it's not about that, but more how they come across visually and with their actions. I get really confused when I meet people like this and I don't want to be rude or disrespectful by outright asking...

I really want to reiterate, I don't mean any of this in a disrespectful way! I know no one owes me an explanation for how they act or dress, but I truly do want to understand better.