Why assume it was the renter's/friend's dog and not some random loose animal? Also, to many people "at the house" means "in the house" - certainly, that's how I interpret it. I wouldn't think twice about a friend stopping by with a dog that remained outside.

The last Airbnb I rented had a "mystery pooper" - gigantic dog poops in the yard every morning. Turns out a neighbor's hound had the run of the area and liked to poop there. I only know it because I heard it outside one night and got the exterior light flipped on just in time. I sure wasn't picking them up - not my dog, not mine to clean up.