Well if there's one thing I learned, it's that I should never trust "sports" documentaries. But that's just me.
Anyway, from what I can remember, he used to do work sets of 120 kg on his squats so yeah, that probably gives him a 1RM at ~2x his bodyweight.
The main factor is probably, again, his way of using momentum and leg pre-load. He's so used to utilize the pre-stretch and pre-load that the run-up gives him that he's not efficient generating voluntary power well at all. That and probably structure etc has something to do with it.
But yeah, you don't need to be good at the standing jumps to be good at the other jumps like you said. If you're into athletics, it's rare to use a bilateral jump anyway, so you need to pretty much focus, in terms of specificity, to the unilateral jump training.