He's been completely alone and hungry for a long time. Take him home and make sure he is warm and has good humidity. Feed him every 5-7 days and allow him to gain weight and be sure he's healthy before handling him. Check out the care sheet on this site. It won't be long before you have a docile BP if you choose to keep him. They are very rewarding pets. Otherwise, try to find someone with experience with snakes to take care of him.

He's just hungry, cold, and afraid I bet.