{See the purple dot in the middle of his right cheek? That's where the cyst is.}
The dermatologist says that it's a cyst, but very unlikely cancerous (because I don't think it's grown in size since I've noticed it, and cancerous cysts typically grow quite rapidly). What likely caused it is that there was a foreign object that entered his skin (could even be like a facial hair being trapped in a scratch/cut on his face) that the body grew a pocket around because it was foreign, causing a cyst. He says they typically don't go away on their own, and that the only way to get rid of it is to remove it surgically. We are going to go back again in 3 months to confirm that it hasn't grown, and then get further details on what surgery would involve.