I just clarified this with AMD and the situation is following.
This value on Navi GPUs is the memory temperature, but it's not the case temperature (T_case) that can be measured on the surface of the chip. It's the junction temperature (Tj) provided by the memory sensor.
Tj is always higher and the difference seen from Tcase can be up-to 18 C (according to measurements done by AMD). The maximum value of Tj here is 105 C.
So users that were concerned about seeing too high temperatures here should not worry about elevated values and not treat this as the surface temperature (which has a limit of 95 C).
I will adjust this value in the next build of HWiNFO so it provides correct description.