Maybe give him some time to adjust and like you said when he knows he is in a loving home and do not need to eat any food he can find as fast as he could, he will mellow down a bit on that? If he gets fat in the meantime, get him to do more exercise will do the trick I think. Just my opinion
I am glad you found him and give him a new lease of life. So many people out there thinks a dog is just a thing and treat them badly. I don't know how some people can do those type of things to a dog because I can't.