Convoked Night Market Lookout generated it's trigger multiple times

Has anyone seen this happen before? Opponent had 4 creatures in play and Convoked 3 of them to play [[Halo Hopper]]. This caused the [[Night Market Lookout]] to trigger at least 15 times. There was nothing in play besides his 4 creatures and my Phrexian Arena. Nothing in the graveyard that would cause multiple triggers.