The entire process shows that there Werner several issues. First did the form for the doctor provide information that certain conditions of a persons health would disqualify the person from diving, was there contact numbers for DAN or similar to help the doctor decide. Most doctors do not understand the conditions experienced diving. As for the dive instructors, few if any have medical training, so how would they understand the divers health and impact to diving. Did the diver after experiencing the first problem decide to continue diving. It is the divers responsibility to decide to dive or not to dive.
As for medication taken for high blood pressure, wrong this does not disqualify you from diving as I have been taking medication since my mid 40's and completed Dive Master in my mid 50's. My dive partner has congestive breathing issues due to asthma and completed the same Dive Master course in her mid 40's.
A medical exam does not mean you are capable to dive and dive instructors can not determine if the person has a medical condition, only that the person is experiencing physical or mental issue.
In the role as Dive Master and AI, I have helped train divers and performed Intro Dives, you can spot divers having issues, but no idea they have a medical issue, only they are having problems which terminates the dive and/or training.