Honestly I'd say he was being dominated in the enclosure with the other beardies, and his foot is due to a nip. It's very common for babies in the tank together at a pet store to suffer stress from the other larger, dominate beardies. They end up getting all the best food, best basking spots, etc. So you end up with a few larger, more active beardies, and a few smaller, more lethargic beardies with feet and tail nips. Very, very common, and the reason they shouldn't be housed together. You haven't had him that long, so he's dealing with normal relocation stress from his new home on top of the aftermath of being dominated the entire time he was at the store...Give him a week or two under proper lighting and temperatures, he'll be fine...