What it means is this:
After the 7 day nomination period, where nominees volunteer for the job, if there are more than 30 nominees only the 30 highest ranking in reputation move on.
The last two elections on AU both had less then 3010 nominees so there wasn't a primary phase though, so everyone just moved into the election phase.
So in other words, low rep users can make into the election, but only if there are less than 30 high rep users.