You can't be arrested for suspicion alone, and bump keys aren't illegal according to California statute, and I didn't find anything about local statues either. So unless they have a warrant out for them, those people are going to walk free. (IANAL)
Also... cars don't use pins, so they wouldn't have been using a bump key for a car, but possibly a jiggler or a blank for impressioning.
Depending on how saavy the local police are, you may get more attention then yoi want if the cops look close enough at your keys.