No, not true.
If you start 4v4 and for some reason a player disconnects, that clan can get a substitute. If they don't have a substitute they may ask the opponent to play 3v3, but they may refuse and take the points.
If both clans agree with 3v3 BEFORE THE MATCH, because they both cant get a 4th player, thats allowed. They may substitute players, but CANT ask the opponent to play 2v2.. We only do 4v4 and 3v3.