Why this particular situation happened in Hawaii is really just a matter of what that particular inspector saw.
I think though that even if the car was a 71 with original bumpers, you still might have failed because it's apparent he never saw a Pantera before and simply does not know what it is SUPPOSED to look like?
I can envision a scenario that if the inspector was comparing say a 74L to a 71, by comparison because of the bumpers, the 71 would look like it didn't conform. Bring your lawyer with lots of pictures and a lawyer who knows about Panteras.
On these cars here in NY now, all the inspector is required to do is walk around the car and look at it.
It doesn't need to be run, the lights don't need to be checked for operation, just visual.
That's very difficult to fail here if the car LOOKS like it conforms.
My '73 has got fiberglass L bumpers on it. No crash cylinder assemblies but the entire car LOOKS stock. Crash testing the car here to see it they work is not required. Not yet and frankly the entire state inspection thing here has been relaxed to the point that as long as the car has no broken glass, lights or bald tires, you are going to pass.
For $12.50, they "ain't going to do a lot".
Best advice is bring a portfolio of pictures with you so that if there is a discussion with the inspector that at least you can have a discussion with him and show him the pictures. Hopefully you also pick a station that the personnel actually like cars as well.