I think the same thing will happen if he does it from a disk 2 save. What I think is happening is basically that the game is trying to load the cutscene based on its location on the disk, in this case, it would be the 1st couple of cutscenes on disk 3, but instead it is loading the first couple on disk 2, because that is where you are(if you check the save file, it still says disk 2), and those cutscenes don't have whatever trigger the game wants to advance to the "elevator goes down" state, so you soft lock.

I think no matter where you have your save, disk 1, 2, 4, it will always trigger the 1st couple of cutscenes from those disks, and the probability that those cutscenes just happen to have whatever trigger the game wants to advance is kinda low I think. Even if you could clip onto the Salt Flats early, I don't think it is possible.