I once saw him charge straight through a bunch of South Africans to score, dragging three of them with him. (He never actually scored a try against the Boks, though.) Big fellow.
I used to figure Jonah wasn't really a freak, just a big south sea island guy - the size of a forward but because he played as a back he concentrated on speed and legs rather than upper body strength. I've met him; he's tall but not a giant.
Then I found out he was actually suffering from a debilitating kidney ailment through most of his career, and started to think, Wow, what would he have been like if he'd been fit?? So he probably was a bit freakish after all.