So pouring molten [anything else] into water would have the same explosive result?
No, I think there's a chemical reaction going on.
Watch the original video I posted above
; he compares the reaction of sodium to this explosion, and they're very different. He concludes that it's a physical reaction, with water entering an indentation in the salt, becoming superheated, expanding and driving the salt bubble outwards, getting it into contact with more water, and so on.