The claim is that, in some cases, the human operators of Deep Blue intervened and played a different move than what the computer indicated (https://www.chess.com/blog/clizaw/did-ibm-cheat-kasparov)

So, yes, you can cheat in a perfect information game.

Nonsense. The operators were weaker than Deep Blue, and Kasparov's reasons for thinking there was cheating are absurd and not based on evidence.

Here, cheated doesn't mean "cheated at chess", but rather "cheated at having the computer play Kasparov unaided"