If it came in a Pro Q box, it's most likely not a knock off. Post up some pictures and we should be able to tell you for sure.
A guy that I bought a few Excel 20's from had the same paint peeling issue on the Excel 20 he had been cooking on. I asked him what had happened and he indicated that he had grilled some CHX at high heat on it the night before.
We've cooked dozens of times on our Excel 20's and have had zero issues with paint peeling. If I had to fathom a guess, I'd have to think you had your fire to hot.