so is the glitching an exploit in the original game or is this some function of an emulator?

^ Both. The glitch is part of the game, but it takes superhuman precision and timing to trigger it, thus tool assisted speedruns are the only means, where you slow down the game, record and rerecord thousands of times until you get the result you want. Still, everything is done through controller input. In this case, the glitch is so difficult to trigger that it apparently took hundreds of thousands of attempts by a computer running for several weeks to finally stumble upon a solution.

In theory, this could be done on an original NES-system as well, if you were said superhuman, with perfect knowledge of the inner workings of the game.

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