They had to win out to stay tied with the Utes to be co-champs. They lost. Utah stands alone atop the south division.
Which as a football achievement isn't great this year, but it's a solid milestone for the program. Being in the top three of the overall conference standings with a chance to win the conference championship is a bigger achievement from the football perspective, if we can pull it out.
But no, there is no south co-championship this year, the Utes are the south champs.