Executive Medicine=leadership positions. Someone with the AQD is supposedly ready for that type of job or has been in that type of job.
The website quoted used to have all the criteria to earn the AQD of which you could complete the vast majority by attending AMDOC. Most of it was experiential (e.g. Dept head). Once you completed all the requirements you could ask for the AQD. How worthwhile having the AQD in your record is debatable.