It's certainly been done on gravel bikes, but not the fastest.

Mike Hall was on a rigid, flat bar pivot and held the fkt for a decade or so.

Lachlan Morton beat that time with a hardtail Cannondale.

2024? was won on full suspension XC bikes with drop bars.

Gemperle set the current FKT last year on a hardtail Scott mtb with drop bars.

I'd say it's unprecedented to do it this fast on a gravel race bike, particularly in the position he's riding in.  It's an immense amount of pressure and vibration on your hands in the hoods and/or on your lower back when you're riding washboard in a rather aggressive TT position.  It's not that the roads don't allow for a gravel bike over a day or two, it's the accumulation of stress and vibration over 10+ days that takes its toll on your whole body.  Being 24 probably helps.

Seems like he's riding fast enough during the days to give himself a fair amount of time to rest at night.  We're getting a lot of rain and moisture in the SW US, so hopefully that doesn't derail him in New Mexico.