I have a feeling something was going on with that family, maybe they were running fast, so to speak, re money or other situation., given that he seems cared for up until then. Maybe one parent won, re the dog, and there wasn't time to find a home. Hard to guess.
Anyway, he lucked out with your finding him!
Of course I'm partial to the fine name, Paco, so similar to my dog's name. Give him a hug from here.