The firearm in question would have to have been in very poor condition, causing it to slam fire, or have been modified for that to happen (or caused by ammo with really unusually sensitive primers, but that seems even less likely). The differences are key enough that it's really hard to do accidentally and I imagine that one prepared for a journalist would not have had its fire control parts mangled ahead of time or its firing pin jammed forward.

That said, if they have an SOT (which they were trying to get) it's entirely possible that it was made full auto from the start.