I think this is the key!
I have the drive set to warn/critical at 60C and 75C, respectively, but Unraid calls these "NVME temperature threshold", not "SSD temperature threshold", which is what I can set in the Disk Settings defaults. If I try to reset the drive's individual settings to its defaults via the Default button, it puts seemingly random numbers in: my standard WD SN770 defaults to 84/88 (its official spec has its maximum operating temperature at 85C) and perhaps more importantly, my Optane drive has -273/-273.
So I think the problem is both that Unraid has weird/wrong defaults and that Disk Location pulls the defaults instead of what the user has actually configured for the drive.