Supporting evidence can be provided to disprove some of those other claims, though. That's why he went with something else. He may have realised it's decidedly more difficult to disprove the potential return of a mysterious creator (I mean, there are entire religions founded on that belief, so clearly some people will easily buy into such a notion without much convincing). And the uneducated masses don't understand that satoshi wouldn't have any direct control over the protocol in the unlikely event they were to return. We know that, but it's not something you can easily provide evidence of to the general populace who may not understand much about software development or consensus mechanisms.
There's an almost devious logic in creating FUD in areas that can't be proven one way or the other. Again, I think Dimon knows exactly what he's doing. It sounds downright stupid to us, but all too plausible to outsiders.