There is a lot of Bullet Magnetism in Destiny and that's a conversation for another day however I can tell you exactly what's going on here. He's using Mida, and Mida's is deceiving we all see the arrow however the actual reticle is a full triangle, Mida fires from the center of the triangle not the tip, if you look at his shots he's not hitting them once they've left the perimeters of a full triangle.