Dear anonymous,136 years ago
It could mean that he was involved in the stealing directly, or that he was able to purchase it from someone who was involved in stealing it. Either way is wrong, but first of all you need to decide whether to break off the friendship. You might want to ask him about it and if he realizes it's a mistake and said it won't happen again then you could give him another chance. If not, and you're no longer friends I would just not associate with him and move on.
Dear anonymous,135 years ago
Haven't you heard the term "Don't look a gift horse in the mouth?" When your friend told you he gave his mom a similar gift, and it had "fallen off the truck," you had the perfect opportunity to ask him what that meant. Instead, you you kept the gift, and wonder if you should call his mother and/or the store. What would you tell them; you think your friend stole some Clappers, wrapped them up and gave them out as gifts? How would that scenario play out if your suspicions are unfounded?
Stop jumping to conclusions about where this gift came from, and talk to your friend about it. Several explanations come to mind in reference to falling off the truck. For instance, trucking companies offer truckloads of damaged, shipped overages, and returned merchandise to their employees as a small benefit. They also negotiate with stores to accept loads of slightly damaged merchandise so the entire profit margin isn't lost. So that gift you got, really could have fallen off the truck so to speak, but you'll never know the answer until you talk directly to your friend.