I never said HCl was a gas. It is a liquid. A liter is a measurement of liquid volume in case you failed chemistry. It stands to reason that a liquid is going to have more moles per liter than a gas.You seem to forget that muriatic acid (aka "HCl") is not a gas. As a gas, which you seem to assume, the standard volume for a gas is 22.4 L per mole (there is some discussion about changing that). It is in solution. Solutions of HCl in water deviate from "ideal" solutions significantly.
I did make a mistake in my previous post. The 6 moles/L figure is for the 20% solution, commonly referred to as Muriatic Acid. The maximum concentration in which HCl is produced is about 38% or 12.39 moles/L. Higher concentrations are possible but the evaporation rate is sufficient to require special storage and handling precautions.