For three way ties (when no team has swept the other two teams), the team with the best conference record doesn't necessarily win the tiebreak. The tiebreak is used to eliminate the third team, and then a head to head tiebreak determines the winner between the two remaining teams. In this scenario, Pittsburgh would have the worst conference record of the two, so they're eliminated from the tiebreak. Then for the SD-Jax matchup, you do a standard head to head tiebreak. Since these two teams didn't play each other, you look to the conference record. And SD would have a better conference record under this scenario.

Also, it should be noted that if two of the three teams are in the same division, then they use a head to head tiebreaker between those two teams, and the winner of that tiebreaker goes through another tiebreaker against the third team.

Yes I'm a nerd.