No, they don't sort them, they make it so that each kernel only has on option for a male parent.. If you only have one bull, there's little doubt about who's the sire of your calves right?
They detassel all plants of one variety (the "dam"), and then plant another variety (the "sire") and (optionally) remove the ears from that one, making the only possible mating a crossbreed. They could leave the ears on the 'male' plants, but that would yield a self-pollinated (purebred) seed in those ears.. Those they would probably harvest separately to plant for next years male plants. In another field a suitable distance away, they'll also plant a smaller area of the variety used for the 'female' plant, and let that one self pollinate for next year's 'female' plants.
I put 'male' and 'female' in quotes, because in corn there is no such thing per se, as both plants will naturally have both sexes, we're only limiting them to one.
It's a bit like a RA bull typically being used over Herf cows to produce a baldy, more often than a Herf bull on RA cows
and yes, hybrids DO occur in nature.. LOTS of them