Hospitals absolutely have plans like this in place. He certainly leaned on his prior experiences to apply lessons learned previously (as we all do), but there was absolutely a plan in place outside of his personal experiences.

The trauma center in our region holds similar "mock incidents" at least once a year. Certainly nothing to this scale (there's just no way to practice that...), but they routinely run drills with dozens of patients and simulate various in-hospital system failures.