Lol dont count on it lol its not always designers that rip if someone sees something they like on google or similar they will use it as their sig alot 2 lol
depends did u make it for him before on this site or something like that lol and is he taking credit for it it might be that someone else ripped it said they made it and hes using something he thinks someone else made
no, he probably didnt even make it in the first place.
as long as youi dont claim it as your own, your clear.
just give credit to the person if you use it