Wow, what a story! I can't remember what famous comedian said, "He ought to be funny, he's using my act." (Was it Rodney Dangerfield? Help me out here). I don't think any creative person is above "borrowing" material, at least subconsciously, and few artists have the integrity or even awareness to go back and ask for permission. Even someone with the awesome stature of George Harrison can be guilty of plagiarism (remember? "My Sweet Lord" = "He's So Fine"), I don't know the details so I don't know if you have a case or not. I think you are wise to take it as a compliment, without any proof, and let it go as your good karma. Hey, I'd buy you a drink on it, just on your say-so. "The first law of creativity is theft" - Bertolt Brecht.