Yeah, that's why I'm just thinking it's not piss because it's painful and difficult to do with a boner or let alone during sex like this. I am a girl too but I do have a husband who has told me it hurts to pee while having a boner or even trying is difficult enough.
I just googled some facts since my facts are a little outdated from you are saying. So for men, the prostate creates clear fluid/precum/natural lubricant for men which would be the squirting substance that can come out for men squirt (though actual piss is rare so possible DG just a rare case lol). And for women, it can be fluids that come from the Skene's gland that is similiar substance to that of men's prostate fluid. But for women squirting can be a variation of this fluid and urine depending how large the gland it since the fluid seems to travel to the bladder for them during orgasm to come out.
You can't pee and ejaculate at the same time lmfao. Your body has restrictions against that so that semen is not contaminated/harmed by urine. Just because they both come out the urethra doesn't mean that they happen simultaneously, similar to how we don't poop during anal sex.