Well, the animal characteristics were based on magic, so that would explain the chameleon abilities. And the human-level savviness can be explained by Dean's mind filling in details on more basic animal-level impressions. When it's a humor episode, more excuses can be made.
We all know why dogs are here. They are here to aid humans in their never ending battle against cats and their attempts to subjugate mankind.
They should have revealed that.