A hot dog is panting, thus swallowing a lot of air. Gulping a bunch of water on top of that can lead to bloat. Drinking water won't do a lot to cool a dog off, but they may WANT to drink a lot. Always best to only allow it in moderation if they have been heavily panting.
I think this is what cause people to blame ice - hot dogs were allowed to drink heavily. The water just happened to be really cold because it was an effort to cool the dog off even more, but all that panting had already led to a belly full of air.