BMI is just an indicator, not an absolute pass/fail test. It is useful as an early screen of people who may have excess body fat, but that's all it does - highlight those who need further examination.
Two candidates could present with identical BMI - one can play a hard game of rugby for 80 minutes, and the other would struggle to get to the fridge from the sofa without pausing for breath, so it's then down to the assessor to work from there.
Using BMI as a pass/fail for an entry medical is crazy, and a very poor use of resources.