I think it's the human player. I always play on insane maps, never less than 40 races...no minors. I have NEVER triggered the UP countdown. I have hit "FOW, and it triggered.
That got me thinking,
I'm not sure where the find x many threshold is, but this is clearly something that needs to scale with number of races. Oninsane maps with dozens of races, it's almost impossible to trigger through other means than ~fow