it sure as hell wasn't good weight. i can put anything on a ridiculous program and have them gain tons of weight too, but how much of that is quality muscle? very little. you can really only gain 1-2 pounds of actual muscle tissue a year on average. so if he gained 20 pounds in 1 month 19.5 pounds of that was fat and water. i also think he is lying to you and was using steroids too.
let's think about this logically.. 20 pounds/month X 12 months means he is on pace to gain 240 pounds in the next year. that would make him the most muscular man on earth. he should be on the phone with the guinness book of world records and having them do a show on him on A&E or something.