Another unknown is where was the Mexicana A319 when it was given takeoff clearance?
If they're using full length the hold short line is not at the departure end so it would take a short amount of time for the A319 to taxi onto the runway.
If you zoom in on the runway I believe it's the perpendicular line, not the 45 degree angled line, where you typically hold short. The perpendicular line is about a plane's length short of the hold short line and the black marks on the taxiway are the deposits from the idling engines sitting at the hold short line.
So instead of just doing a 90 turn onto the runway it requires a slight forward taxi followed by a long, sweeping, 180 degree turn. All of which takes time.