Some clarification.  Shooter entered and first shots were from his semi auto shotgun.  Guy says rifle.  Important because after all 6 rounds were expended, he dropped the shotgun and used his rifle he also brought (slung).

Interesting video though.  Esp. how he mentions it's a learning tool.  So he knows what to do in a similar situation. 

Knockoutlights on IG mentioned he talked a SWAT guy, so someone who has lots of weapons training.  There was a shoot out in a market.  The SWAT guy said he pulled the trigger twice at the target.  The target did not drop, nor did the SWAT guy hear the 2 rounds go off.  So he thought he had a jam.  He then shot at a bag of chips and it exploded (gun working).  By the time he got back on target, the target fell to the ground.  So even the best trained people can have tunnel vision.  Worth mentioning, because possible the NZ shooter also had tunnel vision in his calm state because that 1 guy trying to run away managed to get close enough to knock him down.  He was checking behind himself often after that (gopro's vision went to front then back).