Dudeeeee......And I thought I did sketchy and unorthodox things when working on my car. For a professional mechanic, that is a horrible thing to do. He is a professional!? Even if he forgot to remove the sprocket until he had the cam out, he could have wrapped a piece of timing belt around the sprocket and pinched the belt in a vice to hold the sprocket and cam from moving. Good luck, I'd demand that he front the cost for a new camshaft and take your business elsewhere.