It might be sectors. Multiply the raw value with 512 and then divide by 1024^3 which results in GiB.
Calculating the Total Host Writes this way: 128CADE6C (hex) = 4,979,351,148 (dec) multiplied with 512 (bytes) and divided by 1024^3 gives 2374 GiB, roughly 2.5 TiB. And for the Total Host Reads: 1C66B8F6D (hex) = 7,623,905,133 (dec) which results in 3635 GiB. Both sound reasonable to me. But this might be wrong because these values could represent something else entirely.
It's interesting to see that WD drives can also have SMART attributes F1 and F2. Never seen these on my WD drives, though I don't have WD mobile drives.