First off, good for you for taking him in. It really is sad knowing that there are people out there are like that.
Secondly, I agree with others on here that having his vision checked would probably be a wise decision. Like Smrobs said, if he had been kept in a dark area for an extended period of time it may have made his vision deteriorate. I would wait to decide that it is a behavioral issue until you have had his vision checked.