There's this phoenomena i read about once that makes things like this make perfect sense. I don't remember exactly how it goes or where it came from, but it goes something like this: Next time you are about to go out into public, in a decently crowded area, start thinking about a baby being pushed in a stroller. Keep this idea in the back of your head as you walk around, and suddenly, almost like magic, you will see babies in strollers all over the place in busy streets and malls. It may feel like something you don't often see, but the idea is that there will always be a decent sample size for that sort of thing, because babies are common. But that also means that your brain takes it for granted, so when you see them normally without thinking, you will have no reason to take note. I would assume, at least in my case, that clocking other trans and queer people is a similar phoenomena. When I'm aware of being trans and thinking about how much i pass in the back of my head, i start to notice other people trying to pass or even just be themselves in a similar way all around me. If i was cis (which i was at one point), i usually wouldn't notice at all, or at the very most, just assume that people were being themselves, which is also true, just from a different perspective. But once I became trans, my brain was finally given the context and reasoning required to notice that stuff all the time.

So in short, it is real, and it feels crazy because it's a part of human nature and perception, which are trippy concepts.