The thing is Iran has long promised their max range was 2k Km and so defensive only. This shows that was a lie.

All countries publicly understate the max range that their missiles can go. This is generally understood in the defense community.

What's the point? Naively one would think it is the opposite.

I heard the same about the number and location of French nuclear war heads, or their exact red lines. If you tell the enemy your limit they're gonna sit exactly on it.

To surprise your ennemy. I've heard recently that they tune military hardware differently in peace than in war, e.g. radar signals frequency.