As far as I understood, this estimate is only based on some of the characters and targets stats and skills, but none of the actual damage received or inflicted in combat. The problem with the latter is that it may fluctuate quite a bit, depending on the type and quality of equipment used, or the sort of magic applied. So, yes, the estimate can be misleading. My only advice here is to keep an eye on the previous line about the targets physical appearance. This at least helps to subdivide the mobs into seven coarse categories ranging from "frail and feeble" to "physically perfect".