The greencard system is a mess in this regards. I'm surprised your friend actually tried to travel to the US since one of the first things they tell you once yo

The greencard system is a mess in this regards. I'm surprised your friend actually tried to travel to the US since one of the first things they tell you once you've started the application is not to travel to the US until you have your greencard. It's some sort of twisted logic where ICE thinks that you'll try to jump the line if you travel to the US on a non-immigrant visa.