re: The only point you granted...
Perhaps the combination of aluminum and iron (which is nothing but steel with extra carbon in it) and intense heat created the ingredients for thermite (Iron and Aluminum oxides).
That seems more of a stretch than a conspiracy.
Plus, thermite is iron (or other metal oxide) and powdered aluminum, there would have been no significant iron oxide and whatever might have been there wouldn't just spontaneously mix with pulverized aluminum.
I'm not saying it was planted thermite, but it wasn't a "lucky" coincidence.