Hes probably getting mixed up with Gsync which is DP only with HDMI coming soon or has it already arrived.
I do not believe can, given that it would confuse people. Gsync Premium, or what ever are called the monitors with the Gsync module, only work on DP.
Physically impossible to make them work over HDMI as the scaler won't work.
Freesync monitors, highjacked by Nvidia, are able to do HDMI & DP Adaptive sync. However even if Nvidia could implement it on their cards (drivers), can you imagine the backlash having the expensive "gsync" module monitors not been able to do this, but those for Freesync initially can?
It won't keep consistency to the eco-system and going to be a lot of ridicule.
And here we are on the same thing I have been vilified in this forum by Grim5, Gregster and several other Nvidia fanatics.
When wrote numerous times since 2016, that from Pascal onwards the cards could do Adaptive Sync on Freesync monitors only requiring driver (software) support, they were absolutely adamant that is impossible because blah blah blah.
Now this is happening, they just mumbling through their ignorance....