I don't understand why the Hospital is doing ABGs on healthy adults during a seminar, it is kind of an irrelevant number when you are healthy at the time.
There is nothing at all unusual about the hospital directing this seminar to healthy individuals. It is standard practice in most hospitals and/or medical centres, although the intended audience may vary widely.
Advance medical directives are primarily arranged for the benefit of healthy individuals so that options for treatment are clearly stated in the event a specific treatment could be needed in the future [which is why they are called advance directives].
BTW, advance directives can also specify treatment the individual does NOT want such as when an individual signs an advance directive that hospitals not use resuscitation should diagnoses cardiac conditions develop.