The perk "Vex Stiker" on the VoG helmet for Hunters gives a chance to generate an orb of light for killing a Vex with a critical hit. This can generate an orb when you kill a Minotaur by delivering the final shot in its "head" (the center eyes; it is the part which causes the Minotaur to be stunned and charge you). Even though Minotaurs technically do not have a crit spot since no yellow damage numbers can be recorded, the helmet reads the kill as a critical hit and has a chance to award an orb of light. Maybe the Minotaurs were supposed to have a crit spot originally?