Actually the bots take part of the connection - only upload. Here how I explain. The server know the position of the bots so it doesn't send any packages between the bots (its normal for bots) but it does send the position of each bot to each real player on the server, i.e. costing only some kbps of upload but if there is more bots it cost more, but one bot take much-much less connection and in this case upload, than a real player. But if there is no real players to the server there will not be any packages send (i.e. idle connection).
