One thing that is odd to me is that his helmet looks substantially cleaner than his clothing. The soiling on his clothes initially made me think he may have been living on the streets, but the helmet looks clean and undamaged. This could just mean that he only recently came across the helmet, but it could also mean that he's just been wearing the same clothes for several days or weeks and put the helmet on only once he decided to leave his home. He looks well nourished, not emaciated, so despite the condition of his clothing he looks like someone must have been caring for him (or that he is relatively independent in his ability to obtain and safely eat food). I would be concerned about the well being of his caregiver, as it is not uncommon for people with developmental disabilities to be cared for by single aging family members and if that caregiver becomes incapacitated there is not always someone around to help the child/adult. The area where he was found is densely residential, though, which I'd think would increase the probability of neighbors recognizing him if that were the case.
**Editing to add that since he also has a clean soccer ball in the photo, it just occured to me that the ball and helmet may not actually be items he was found with but rather things that LE keep in their vehicles for children in distress, like the Hug Patrol program.