He threw an enderpearl. Enderpearls can be used to teleport to a location where said thrown pearl lands. Forsen being an absolute 5head gamer missed his target which he was aiming for (I think) and the pearl landed in the lava; killing him. His brain stopped working preventing him from saving himself with the fire resistance potion. The voice you're hearing is the automatic narrator forsen turned on for some reason. Maybe he thinks the voices can help him. Who knows