I think the problem is that there were no money in the "pot" and you were the only one who bet during the match. And since you've bet for a player and no one else have did, that tc goes into the pot and the winner of the bet get's the winning pot.

Example: You bet 500 tc for player 'A' to win and no one else have placed a bet other than you. The tc bets gathers in a pot for the winning bets.
Player 'A' wins, you win the tc in the pot. So technically, you aren't betting against an invisible player but instead, the entire users who bets.