Yes the panel rate is always 120 on a 120 screen.

Why? Because to do the tricks a 120 Hz screen does and more the panel is refreshed 120 times a second. The on screen indication is for the inputs. Imagine if it was the panel rate or showed both. 1. If it showed both then folk would ask why it never changes. 2. If it showed only the panel rate then folk would ask why they don't see the input rate.

So it shows the input rate.

And again, why 120? Because at 120 you can play 24p content. And don't be put off by those that want to debate "proper" 24p playback. I won't enter that discussion here.
Bob