Legal Question in Construction Law in California

Ever? Sure. If they set the forms, do the pour, and finish the surface, they're a contractor. If all they do is show up with a truck full of concrete and dump it where told, then they're not. On major engineering projects the general contractor may even establish their own on-site batch plant and become both the concrete supplier and the general contractor.

I guess the short answer would be yes. However, this is only because (a) any person or business can be or become a contractor based upon what they do, rather than what they call themselves, and (b) for some purposes, suppliers to a job have rights similar to contractors with respect to mechanics' liens and similar matters. So, I suppose really giving a definitive answer requires knowing "What happened?" and "For what purpose?"