If your plan is to demolish a building covertly, then don't be so obvious about it. Leave some of the structure intact so you can use it to make the very point you're trying to make.
Remaining structure doesn't explain the molten metal, the obvious effort of getting rid of the evidence as swiftly as possible by quickly hauling it away and destroying it beyond future investigation by cremation. It doesn't explain away all the witnesses that heard explosions seconds before the collapse, etc., etc., etc.
I was as skeptical as you when I first heard it was a planned demo, but after hearing all the evidence, I find it credible and most likely.