Unless you drank A LOT of water that morning, I highly doubt that any amount of pee would be recognizable as such by the time it reached one of the oceans. But the guy was 100% correct. Any water landing on the East side of the Continental Divide ends up in the Atlantic, while any water on the West side ends up in the Pacific....and if you were standing there with a full bladder, you could decide where it was going to go. As the crow flies, it's about 1000 miles to the Pacific Ocean, and about 1700 miles to the Atlantic. Standing on top of the Continental Divide, you can't see either ocean, but that's the final destination nonetheless.
We make decisions like that every day. We can't actually see where that decision will end up, but it will end up there regardless. Sometimes it takes someone else (even a total stranger) to stop by and tell us where a decision might lead. But if that happens, will we listen? Will we make an adjustment? Or will we continue making the choices we want to despite knowing the outcome?
If you were to pick up a cigarette and someone tell you that smoking leads to cancer, would you still smoke? If you were to pick up a can of soda and someone tell you that drinking soda leads to obesity, would you still drink it? If you were about to throw some plastic away and someone tell you that it damages the earth's ecosystem, would you still throw it away?
I understand that you have to trust that the person is telling you the truth, but if you know the information is accurate and the person is trustworthy, why would you ignore it?