I used to take Babykins to a doggie social where dogs ran around, chased thrown toys, wrestled etc. None of the dogs smelled like pee. Some dogs were not well potty trained and would pee and poop inside the building but it was cleaned up quickly. Play excitement can arouse the need to potty in a dog that recently pottied so its definitely possible some or more than one dog is peeing. Babykins had to pee before we went inside as did most of the other dogs, she also would pee and poop afterwards when we left, but I was the only one who left to building half way through the hour to allow my dog to potty outside Which is why she never made inside the building...so that was 3 productive potty sessions in about 1 hour and 15 minutes.
it’s also possible some part of some dog is under the pee stream? I know my minipoo was once peed on by ano dog when she got too close.....which meant a quick March home for a spot bath, and a more diligent mom not to allow her too close to dogs when peeing.
I go to dog training facilities regularly where tons of dogs potty near the entrance, it never smells unless someone didn’t pick up poop. I would find it odd that two dogs could cause a smelly backyard, but if they peed on toys, even by accident, I can definitely understand the need to wash them.