More believable, but less fun. Still, the guy was using lighter tippet than if he was fishing a big articulated streamer. While a beast on a #20 fly is impressive, trout eats fly then gets eaten by bigger trout is pretty cool, too.
The 2 truly large trout (well over 2 feet long) I've heard of coming from the Delaware ate smaller fish:
1. 32", 15 lb. (I think) hook jawed brown caught some time around the late 90s near Deposit on a white Zonker (alewife fly). Photo used to be on display at Rainbow Outfitters near the 191 bridge. I can see that photo when I close my eyes. What a beast!
2. The "Food Chain Brown" from the OP.
These are the 2 very rare, very large browns I am aware of.