I'd be inclined to say it was plug. They do happen occassionally but usually they clean themselves.
Try wrap him in a blanket to turn him over and chek he isnt inflamed around the area.
A warmed wet cotton bud around the opening can clean it if he hasn't managed and allow you to look. With older hams they sometimes need "popped" to clean the plugs out but he is young o hopefully you just had him out before he had finished hi cleaning
