I think they're, somewhat poorly, referring to what is called a "G-Sync Ultimate" monitor. These monitors contain an expensive proprietary hardware module that facilitates frame syncing. It's not necessary though, Nvidia firmly lost the marketing battle to AMD there. This monitor has the frame syncing support you want.

I am not sure if it is still true, but originally g-sync 'ultimate' moniters with hardware were able compensate better for lower refresh rates. FreeSync kicked in at higher refresh rates.