How do they know nobody exited the pool to pee?

I’m assuming it’s a smaller pool where they can see everyone

Like did they exit and they assume they didn’t pee or did they not exit at all and therefore must have peed in the pool.

My interpretation was the latter

I have a great bladder, the greatest bladder in fact lol. Really though I can go more than 4 hours without peeing.

Maybe everyone is drinking so holding it is unlikely?