Some gym people shouldn’t be classed as people and I say that as a gym person.

I've been on the other side of that situation. Usually the story is something along the lines of looking back to see someone is following, misjudging how long it will actually take to reach the door, struggling to decide whether to wait and then totally fumbling the door and walking off in shame because I completely messed up what should have been a straightforward interaction. Now that I'm older I'm less stressed about that sort of thing and would probably apologise for totally messing up the door holding thing, but when I was younger I would have been too overwhelmed by messing up the first interaction.

Of course that person could just have been a dick, in which case fuck them and I hope they stub their toe on an exercise bike.