Your text you are quoting is dealing with ambulance flight... i.e. flights where the passenger was ill and a risk is being taken transporting him or her from the start of the flight. The text you are quoting is just saying that such flights are being giver higher priority than regular flights. These flights are not in distress per se and equipped/staffed to handle the patient during flight.
An in-flight medical emergency, where a healthy passenger boarded the flight, but is experiencing medial problem during the flight is, however, an emergency.
ICAO Annex 2 Rules of the air:
3.6.2 Adherence to flight plan
3.6.2.1 Except as provided for in 3.6.2.2 and 3.6.2.4, an aircraft shall adhere to the current flight plan or the applicable portion of a current flight plan submitted for a controlled flight unless a request for a change has been made and clearance obtained from the appropriate air traffic control unit, or unless an emergency situation arises which necessitates immediate action by the aircraft, in which event as soon as circumstances permit, after such emergency authority is exercised, the appropriate air traffic services unit shall be notified of the action taken and that this action has been taken under emergency authority.
The potential death of another human being, in my opinion, warrants deviating from my clearance.
I can accept to land as no 2, behind the guys with the cabin fire, as the death of more human beings is worse than the death of one. But I am not waiting for the controller to do his routing radio transmissions. I guess we are going to have to agree to disagree on that. My passenger hopefully lives to see another day. Yours?
P.s.
MAYDAY is according to my OM-A mandatory in case of a medical emergency. Of course the PIC deems when it's a medical incident and when it's a full blown emergency. A precautionary diversion, like the Austrian example above, is in my opinion definitely an emergency.