during particularly intense orgasms pelvic muscle contractions can squeeze the bladder and pee comes out

it's not uncommon (or harmful in any way)

some porn stars learn to do this intentionally and there's some slang name for it. some perverted men search pornhub for it.

most women are really embarrassed when it happens and rarely talk about it. so it's understandable that some of the public doesn't even know it's a thing.