If her body was ever in the van, that is.
I think it’s more likely they camped a few days hike away from where the van was parked, then whatever happens, happens, Brian walks to the car park on his own, gets a lift, planning to steal the TikToker’s car, panics, goes back for the van and begins his drive back to FL.
Narrative he was maybe hoping to pull off was “Looks like she parked up and went off on her own hiking for a few days to a place with no service, then got lost and had no water. What a tragic accident”, while he says, “Yeah, we broke up and I made my way back to Florida. I know where her van might be parked, as it’s the last place I saw her when she dumped poor me!!”
“Yosemite” is perhaps a deliberate two-in-one diversion + attempted division of resources?