Before opening the door ``Check outside for hazards!`` is part of the drill. Probably no hazard detected directly at 1L and 4L therefore doors opened and slides deployed, Note no-one evacuated down those LH slides, and because of obvious hazards at 2L and 3L those weren`t opened. Once hazards detected you will have seen reports of crew saying ``Not safe`` and redirecting to alternative exits .It is also possible a late call to evacuate right hand side of aircraft only was made.
Fantastic job by CC it seems. You could have seen CC on the ground after evac and all well away from the aircraft checking on passenger welfare. Also note reports that crew did not leave the aircraft until they had checked all passengers were off. Seems like a text book evacuation to me.