An element of truth exists. Most likely deaths and maiming would have occurred with guns. Tannerite is not that energetic. Even black powder would gave been worse.
Is it known that tannerite was the BCompound used?
KYPD
Tannerite is very energetic, it is just a bit difficult to detonate.
Tannerite is just ammonia nitrate and powdered aluminum.
I doubt that we know just what the explosive used was, yet.