The spongey tissue gets wrung out violently during an orgasm and thus a squirt comes out. The force of a squirt is stronger than pissing and it comes out in one go like a bucket being thrown at you, not in a nice stream like a piss.

Anyway I don't really care what Mr.aus thinks he obviously has no idea, but I'm happy for him to stick to his head in the stand position since it is one less wanker trying to make a girl squirt, I'm pretty sure he couldn't do it even if he tried, if his juvenile aggresive attitude is anything to go by.