I just have a hard time believing that he ran as fast as he could during that relay, even if he did have a stomach issue.
I believe if you agree to run on a relay team you must give your best effort because others are depending on you to do so. Many times individuals run better legs on a relay than they can individually due to the extra motivation being on a team provides.
If either he or the coach decided not to give full effort, it was wrong. At least gut it out during a big kick to run 4 seconds faster to avoid having your team finish last.
Normally when I have stomach issues they first appear during the warm up or before, and not suddenly during the race.
Part of this had to do with scheduling. In a regular track meet, the only relay that could take anything out of you (4X400) is the last event on the meet schedule. You run your individual event as hard as you can, and then come back and run the relay even harder because there is nothing to save it for and others depend on you.
If they are going to have a DMR do it the last day before the 4X400.