It does sound like a hernia, and while some are harmless they can be a major issue. Tissue can come through the hole and be strangled which is not only extremely painful but it can die and release toxins if not caught and repaired soon.
If you have a vet visit planned soon anyways keep a eye on it and if it changes in any way get him to the vet. If not, get a vet visit planned so it can be checked out and diagnosed
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