So due to a topic earlier today about an addon which uses /who queries to find out population on each realm, it brought to my attention to test it out and see what is going on especially since there was no data presented in that topic (Firemaw), I did a few tests myself while changing layers and I found out that /who is related to your layer and not your realm. A simple test:
Before asking to change layer:
i.imgur.com/TWFnSEI.png
After changing layer (mobs around me changed so I made sure it was a new layer):
i.imgur.com/0TCQGNK.png
So the data given from CensusPlus is on your current layer only. For me today it said that 6000 players were online on alliance on Firemaw, but thinking now, maybe that was just on my layer. So I made this topic to see if others thinks this is logical and realistic or if the addon was correct to say that there are only 6000 players from 23:00 - 01:00 playing, on alliance?