Some things I'd say were bordering on "ripping off" would be the starting room, which looks similar and has a bag with flies which is reminiscent of the talking paper bag, it's even in the same spot.
Later in the game the radio asks you something along the lines of "are you sure you're really you?" which is also akin to the paper bag in P.T. saying "Are you sure the only you is you?"
Then there's the radio which details a gruesome crime, the looping hall, the "look behind you", you get the point.
I think alone all these elements are fine, but when you use them all together it does feel uninspired.
I actually did not realize the game was a spoof. So given that, the copying would be fine, if the game was really trying to be a spoof. Spoofs are supposed to be a humorous imitation. This is not. It's just an imitation.