I don't think he ever forgot that he was no longer in his home, was out on the street, and was hungry and thirsty. He'll never refuse the opportunity to go out; his tail wags, and he comes right over to have his collar put on. The not forgetting part comes just before I open the door. He won't leave until he checks his food dish and eats what ever he left over from the prior meal. Then he takes lots of laps of water. Only then does he go out the door.
When BJ does that I get a little sad because I think that he remembers when he was on the streets, hungry. and had to scrounge hungry. He's afraid of that and to be sure is has has eaten and had water.