My own theory is that he used his previous infection with lots of medical backing to get his exemption.
Keep in mind that rhe 180 day number (for previous infection) is an average based on a population size cohort. This is derived by modelling antibody levels of infected people (over various populations) and establishing a baseline of what antibody levels are "high enough" to offer protection. This is somewhat subjective as it does require expert medical judgment.
If he can show that his antibody levels now are higher than needed (vs the population size studies) I could see medical experts accepting it under a blind submission basis.
Thats were it gets sticky though.
The panel is accepting the antibody lab tests at face value. These could have been cooked.