Your are right! There is actually a very high "primary hard drive" score. I get a score of 7,4, see here. There is no way you can reach this with a classical hard drive. The best score you could get in such a case was a 5,9 as far as I know.
According to an answer here: Defrag Detects RAID-0 HDD as SSD, the Windows defrag utility actually relies on the WinSAT score to classify a disk as either SSD or HDD.
I tried it out and tweaked my "randomreaddiskscore" to a much lower value, then the defrag utility indeed recognizes my drive as HDD again.
So it's a design issue of Windows, and not VMware's fault. But maybe VMware could provide a workaround for this?