This indicates that the host's game has crashed or been closed.

I kept chatting with the host for the entire game, cuz chat was the only accessible thing then they completed the mission

That's very strange. Were you downed before/after joining back? Also, were you close to any structures/small terrain crevices when you disconnected? Usually the game will teleport you back to the surface after falling through the ground like this, so this is a rare case.