Emergency runway is too close to the main runway to be used in this case. There will be people everywhere on the ground, lots of debris ( taken off by pax I.e bags, papers, rubbish ) all over the place, so until the runway is clear and clean, the emergency one would not be used.
And well done to the virgin crew who were on the flight, they got everyone off quickly and effiiciently, and their day has only just begun. They will now be caught up in hours of debriefs, paperwork etc , reliving this 90 seconds of trauma for hours to come.