Is this stoichiometric question answerable? (unknown variable)
With a lot of assumptions, 0.5 M is a reasonable answer.
Here are the holes you have to fill in.

If it is a titration of NaOH and HCl, it is probably an acid/base titration where we stop the titration when the pH is neutral.

Titrations are often performed to figure out the concentration of a solution. You would titrate a smaller sample of the solution to figure out the concentration. Technically, the concentration of HCl after the titration is zero because all of it is supposed to react as you reach the endpoint of the titration. So it makes sense to ask about the concentration in the original solution.

The stoichiometry of the neutralization of HCl and NaOH is one-to-one:
$$\ce{NaOH(aq) + HCl(aq) -&gt; H2O(l) + Na+(aq) + Cl-(aq)}$$


Of course, it is silly not to give any context when posing such a question on a quiz. I won't comment on the statements you attribute to your teacher other than to say that hydrochloric acid always contains water (pure HCl is a gas under ambient conditions).