Still trying to make sense of this episode, especially regarding the dog(s) and I am relieved that they did not have a scenario where an animal was injured. Nash had done some strong hinting that Colin fans would be in for a rough time so I was concerned there.
Everything was ok until Maggie got "Colin" out of her car and Gary appeared. Gary had already said goodbye, it was emotional and painful and it should have stopped there. Returning "Wesley", who proved he knew his name at the park, was the correct albeit painful thing to do. I did notice that the dog, in this case supposed to be Colin, did not recognize the neighborhood, the house or the woman. No way that would have happened. And the dog didn't seem to know Gary either, Gary should have realized something was wrong although I suppose we can chalk that up to his being so distraught. Maybe the dog was just a bad actor?
So here we are. Gary did not switch the dogs, Maggie did. Once he found out Gary seems to believe that the "old" woman wouldn't know, That's on him. At this point once Gary thinks it over he should take Colin back and swap him for the rescue dog admitting there was a mix-up with two similar dogs. He should ask for visiting rights with Colin/Wesley and he should adopt the rescue animal.