Chemical change

He got banned for committing a logical fallacy. His argument is:

If concrete is a liquid, then it pours.
It pours, therefore concrete is a liquid.

But P -> Q <=/=> Q -> P. He is affirming the consequent.

Justified ban IMO

Isn’t concrete, when purchased in bags, a powder? Wouldn’t you need to mix it before it could cure and harden? I would think he’d just be throwing dust around.