As LycanGalen says, it's kind of pee, in the sense that it comes from the bladder and goes out the peehole.

But pee is strictly speaking waste filtered by the kidneys, with enough urea, ammonia and other stuff in it. And pretty much every single scientifically done testing showed trace amounts of it in squirt.

Think of it like this: you have a "well seasoned" tea mug, with thick, solidified tea residue on its walls, so solid it barely comes off even if you scrape it. You take this cup, fill it with water. Is that water now tea just because it has some marginal tea residue in it?

Well, it's sort of pee. It's got the same chemicals in it that our body puts in urine, plus excretions from the skene's glands, which are related to the prostate in guys. It also isn't carrying waste from the kidneys, so it's "clean" pee, if that makes sense. Same idea as how cum and pre-cum overlap, but aren't the exact same thing.