With all due respect, that’s nonsense.
A truck is no more or less an instrument than a firearm. In fact, as we’ve seen recently in England and France, if used properly, a truck is a far more DANGEROUS instrument than a firearm.
The difference is in how you perceive the truck and the gun. You want liability for one and not for the other.
Now, you could make the argument that the gun is created for the purpose in which it was used while the truck was not, but that doesn’t hold water either. No ones making a gun for the purpose of murder, just as no ones making the truck for that purpose. Guns are made for sport and self protection.