What they do is in Ollie's class there would be a separation for male & female. So one female & one male could get a 1st. They then compete for BOB. So you get a BOB for each class available in the opens. All the BOBs in each section (like neuter or kitten) compete for Best of Variety Kitten/Neuter/Adult & then there is a best overall that gets taken to a new pen for BIS judging.

Often it is possible to have one cat entered in a class (like silver tabby series Maine Coon) & have nothing to compete against in the other gender.

If you look at a schedule it will state the judges at the start of the varieties & also for the overall best. They will usually decide on BOV during the day & once decided at the end they put them in the pens & have the show manager on a mic telling everyone what is going on & who won etc. Did you not see this?