HWmonitor is rarely accurate about anything in my experience. If you want to monitor pump speed, and if the pump is connected to a motherboard header, then check the data in the BIOS for that header. It will be accurate, unlike the readings from HWmonitor most of the time.
Or, try HWinfo. HWinfo, again, in MY experience and in the shared experiences of a lot of members here who have related similar problems on a good many chipsets, is a lot more accurate than most of what is out there. It's kept religiously up to date in terms of chipset support.
Since the maximum pump RPM for that cooler is around 1450rpm, there's no way it could actually be at 4891rpm and not have already burned up, if in fact it could ever even REACH that RPM, which is seriously doubtful.