Conceding is not based on majority vote.
My post from another thread:
If a person leaves the game it automatically adds a vote to concede for that player, so you will get the message that the leaver is requesting a concede (even though they quit, not conceded).
All players on a team must click concede to end the game. AIs are not counted.
If you are the last person to hit concede you should not see the "player has requested to concede" message.
If all players on one team quit that team automatically concedes and the game ends.