nope that's why I said it was wrong..... 
at some point it got turned around in meaning 
The way it was explained to me is this: thumbs up = death/use your weapon, thumbs down = life/sheath your weapon (just like ink said). This makes us think that thumbs up was a bad sign back then (and of course it was for the downed fighter), but since this thumbs up/down gesture was used to determine the ultimate end to a bloody fight for
entertainment of a crowd; of course the crowd would see a thumbs down as a bad sign because it was less fun to watch. So as far as the crowd was concerned thumbs up = good, thumbs down = bad. If you look at the meaning of the gestures from the perspective of the spectators (which if you think about it the whole thumb up/down was always just a way to play to the crowd), I don't think there ever was a switch in meaning of the gesture.
......aaaaaand -1 to the OP, I spend too much time getting shot down anyway. I wouldn't play if there was a respawn wait time.