I would say he was someone's pet either lost accidentally (during the flood?) or released after they didn't want him and that's how you ended up with him.
To know what to do now would depend on what you want to do with him, keep him? or find a new home for him? If you decide to keep him, I suggest reading up on here and the main site for all the info needed to maintain a healthy habitat for him. If you can't or don't keep him, I would try to place him with an animal shelter/rescue group that can care for him and find him a new home. I wouldn't just let him go in the wild since he's not native to your region.
Good luck and let us know how things go.
