Maybe related - someone did a test some years back - took a handful of people into a room and let a dog in. Everyone ignored the dog except for one person, who petted it up and paid positive, emotional attention to it.

The a few years later, they took the same dog to a room of people and the "nice guy" was one of them. In every case, the dog "remembered" the "nice guy" and acted familiar with him.

Wish I could cite the actual test, simply can't remember where I read it (Maybe a Desmond Morris book? The guy who writes the animal behavior books), but it seems to play along with dogs having a "world" of scent information that's unimaginable to us. I guess if they have decent memories, there's a survival advantage in remembering a friendly scent.