Unsolved mystery!

Given the low temps we’ve had in December, our chicks are in mobile brooders in the basement. One night I needed a tool and headed downstairs after lights out. I thought I’d peek in on the little ones and was completely baffled by what I saw. The bin of barred rocks, fluffy and sleeping. These guys, fully wet as if they’d just taken showers in a tiny chicken locker room somewhere. Bedding was dry. No leaks in the ceiling. Waterer is too small for a bath, much less all of them at the same time? All of them were uniformly wet, cold and shaking. I wrapped each one in a clean rag and brought them upstairs to dry off by the stove. Still can’t imagine what happened. Any chicken detectives out there with a theory? We’d love to hear it.