This became a new rule this year for postseason games. As the ref explained at midfield they were starting a new game with both teams getting at least one possession unless there was a defensive score on a turnover on the first teams possession. Had the first overtime period expired they would have reversed field direction and started a new quarter. The game would not have ended in a tie. Once both teams had a possession they would have played until one of the two teams scored no matter how long it took.