Not sure, there is at least one pair of tickets together available now so its not the only singles remaining standard either. Guessing in this case it was more a marketing ploy to get some additional media coverage. Looks to be maybe 100-200 seats available max so I'm sure it will actually be sold out by kickoff regardless.
Remember a few years back when Barta announced an iowa game was sold out and yet you could still buy 20 tickets together online up until kickoff and a few thousand fans, all sitting in the same sections, decided to come dressed as empty seats? yeah, this isn't anything as egregious as that. Or nebraska's fake sellout streak.