I would have preferred a true PGA member to win but at least it wasn't Dechambeau! Can't stand that dude.Pretty sure a non-PGA Tour member has previously won. Looking back, Martin Kaymer won in 2010 and was on the European Tour. He then turned down the PGA Tour full time until 2013. There are multiple ways to qualify, and some are not PGA members.
Edit: Plus, this is the major for the PGA of America, not PGA Tour.
Koepka would have never left the PGA if he wasn't having serious issues with his knee.