The motor glider in PLAYERUNKNOWN'S BATTLEGROUNDS is not an armored vehicle. In fact, it is one of the most delicate vehicles in the battle royale. Despite that, this player managed to turn the glider into a deadly bomber.
Usually C4 is placed or thrown onto nearby objects, not thrown out the side of a motor glider. The physics of throwing C4 is much different than throwing a grenade so accurately throwing C4 from a distance, let alone while moving at a considerable speed, is difficult.
Taking this into consideration, after spotting a drop, Crumblestache seizes the opportunity to catch enemy players unaware. The Redditor waits for just the right moment and switches to the passenger seat which allows them to throw the C4 at the drop. It is hard to tell where the C4 lands but one can assume it landed within the vicinity of the drop. After Crumblestache flies away from the drop, the C4 explodes and kills a player.
Whether the C4 landed in the grass near the drop or on the drop, throwing the C4 at the right time and securing a kill was no easy feat.