The disk is disabled so it needs to be rebuilt.
Unraid disables a disk when a write to it fails. But that write still updates parity, so that write can be recovered from a rebuild. After a disk is disabled, Unraid doesn't use the disk anymore. Instead it emulates the disk using all other disks from the parity calculation. The emulated disk can be read, and it can also be written by updating parity. So any subsequent writes are also in the array and can be recovered.
The actual disk itself is out-of-sync with parity. The only other possible course of action would be to New Config and rebuild the parity disk instead. But since the data disk is out-of-sync and missing those writes, it really makes more sense to rebuild it.