Either bad luck or wtf are you reading
It's hyperbole, but while I haven't taken note of the names of the comics, I have noticed that there is an oddly high amount of comics that just have a random moment of watersports fetishism coming from japan.
The only one that comes off the top of my head is Golden Boy, and his obsessions with the women's toilets, but there's plenty more moments that come from comics that aren't particularly erotic or sexual at all. It'll be some random cliche isekai, but suddenly a girl will someone 'accidentally' end up peeing on the isekai... actually quite similar to what happened here in this chapter, haha.
I also vaguely recall ANOTHER isekai where the MC pissed (lol) off a dryad by peeing on a tree that turned out to be said dryad (and then proceeded to pee on her several more times, somehow).
And just to make my point clearer - I can't think of a single instance where I've read or seen a out of nowhere fetishistic piss joke in western media, so this feels like a bit of a Japanese thing.
Either that, or yeah, odd 'luck' of the draw.