I don't have any issue with what Watson said - for a couple of reasons:
1. Its a press conference, and I'm going to take anything a coach says with a grain of salt - especialy if its an answer to a question that could be seen as a bit absurd. I don't expect any coach to be entirely honest in a press conference - by nature these guys think what they do is top secret.
2. Play calls are based on down/distance/score/time, and sub packages mirror that. This is mostly on the position coaches. Teams go into the games with packages for each down and distance (depending on game situations). The position coach should know who is supposed to be out there in each situation and should be subbing accordingly. If a team plays with any tempo at all the play call is coming in about as soon as the next play has just finished - the position coach should be the one shuttling players in and out.