I'd have let it be. It isn't often you can get away with that, so he likely couldn't do it twice. You paid a ton of money to be at that park, and the last thing I'd want to be is a Karen in that situation.
Here is a good example of a time when I had a Karen in my line and I actually was NOT in the wrong. Haunted Mansion line, we skipped the fireworks to get in to some rides we hadn't done yet. So we are in line, my wife and kids felt they had enough time to run out onto the main walkway and see the fireworks the best they could. 5 minutes or so. Well, the line was going faster than I thought so I had another relative with me and he stayed in line while I went to go get them and bring them back. They were coming back anyway, and so I was gone for 10 seconds out of the line, but still had someone in our place. We come back and get in the line and a young guy and his girlfriend(?) start complaining to me that I cut in. He's in a wheelchair and as I am trying to get past him his girlfriend actually tries to run me over. I was pretty surprised and tried to tell him that we had someone in our place and I was just getting my kids. He was a classic Karen, didn't listen to reason, and he complained to a cast member who sort of just smiled at me as if to say "Yeah don't worry, I think the guy is an idiot too." I explained it to her and left it at that. Here is the kicker, we all ended up in the same stretch room so nothing changed one way or another.
Then I noticed he got up rather comfortably from his wheelchair and got onto the ride vehicle. Hmmm. Interesting.
Anyway, the point is that WDW is the last place I want to start a verbal fight with anyone.