Maybe he's just a fan of mime.

There could be a slightly traumatic, considerably less cute backstory to this dog's relationship with the glass door. It's possible that he's already smashed his already smushed face one too many times, and isn't stepping into the house till he's certain the door is open. He's so apprehensive, even his owner's word isn't good enough for him. A human arm turning the knob and "pulling" the door is what he's waiting for. And it looks as though he's willing to wait all afternoon if he has to. Why not, it's a beautiful day and it's not like he has to be anywhere.