Did you place Bridge in the lineup anywhere? If not... once it hit blowout time, he is going to come into the game for someone. It just so happened to be your SG.
In order to maximize your chance to get your player 48 minutes in a game, you can't have someone sitting on your bench that is not in the lineup somewhere (bench or reserve). If Bridge had been in the lineup (or was sitting in the stands somewhere), your new SG had a greater possibility (but not a 100% possibility) of playing 48 minutes.
In any case, this is not a bug.