As far as I'm aware, those percentages relate to the health of the drives. I'm not 100% positive on this, but when I discovered it myself a few weeks ago (been a while since I'd used Speedfan before that) it seemed to roughly correspond with the drive's health/performance ratings in the SMART tab.
Remember that the Exotics feature, as it says at the bottom, is still in beta stage, so it may not even relate to anything.