First, make sure you have a level playing field.
If he asks you to provide statistics that banning guns increase crime, ask him to provide statistics that banning guns lowers crime.
To give him the benefit of the doubt, he may already know that no study shows either position, and he's trying to teach you that letting the opponent in a debate pin you down on statistics is a losing position; the valid, corresponding tactic is to hold them to the same standard.
Debators often want to put you at a disadvantage: it's "obvious" that banning guns lowers crime, so if you think it lowers crime, you need statistics. In other words, let's assume my position is true, but you have to "prove" your position. And the standards of proof I will impose on you will be impossible to meet. So you lose before you start, if you let the opponent dictate the terms of the argument.
The goal of a debate is not to prove; it is to argue and persuade. You will have many arguments that banning guns is bad for individuals and society; you will have little proof.
As to the result: congratulations to you, and kudos to him.