It seems to me that if “tapes” existed, there would be no reason to refrain from leaking them, or publicly releasing them. Why threaten someone with, “hope there aren’t any tapes…” if not to intimidate them into silence? You don’t say, “If you don’t behave, I might have to defend myself,” you just come out and defend yourself.
Comey is a bit of a clown, it’s true. But I seriously doubt that an FBI agent-turned director of the entire agency would be totally unaware of the possibility of being taped, even if illegal. Being aware of such possibilities is kind of their whole shtick. If he did say something on a tape which he then lied about later, he’d dumber than he looks.