looks like 2 house's brought together. I'll guess the newest addition is the house on the left and the orignal is the one with dormer(?) like your other photo [link] I do not know why but I would check out the "summer" kitchen first as that peaks my curiosity or my be I'm just hungry right now lol
the "L" shape of the house was common in this area many years ago. Even a few of the stone houses I have photographed follow this design. If that is the case, then it would not be an "add on house", but really there is no way to know, so you suggestion may very well be correct. The summer kitchen is a really neat addition and does need to be explored, though likely not by myself.