Hi andy10 and welcome to the forum!
Crohn's can be so tricky. Sometimes you feel fine or better and other times you're in extreme pain etc. Chances are that he's dealing with scar tissue as well as inflammation and even if the inflammation goes down, the scar tissue is still there and can present problems in the future (blockages etc).
Before my surgery I was feeling perfectly fine. That's a good thing though. You really don't want to wait until its an emergency to have surgery and you also don't want to feel completely miserable until your surgery date. Often times we feel better because we changed our diet so dramatically that its reduced our symptoms a lot. Eating smaller, softer, low residue meals can help reduce symptoms along with going on a liquid diet. I was on a liquid diet before my surgery because I kept having partial blockages over and over from inflammation and scar tissue.
Even though I was feeling better they did imaging tests prior and knew exactly where they needed to cut out. Surgeons aren't going in there blind looking for problem areas, they know exactly where to go and if they find more than expected while they're in there then they will remove that as well. So don't worry about that.
Thank you for looking out for your friend. I'm sure he appreciates it. He's lucky to have a friend like you.