That is incorrect. For the majority of the minutes it used my SF who makes at least 7k less than the backup PF.
My experience mostly has been that the coach chooses the player backing up the player least likely to come out of the game - i.e., if I have a PG with high stamina and GS who is likely to get the most minutes, whoever his backup is will replace the injured player - though I've also seen them rotate through a lot of players. I've never tracked the minutes on early injuries enough to see if it may be trying to get the players who have been in the game the least into the game instead and that may be why several players seem to rotate in, or if it's just related to getting players in and then out to their natural position.