I disagree with your logic: the fact that there are (even possibly a majority!) of cases when not wanting to live as long as possible is the result of a pathology, it doesn't negate that there are perfectly sane people who do not want to prolongue their life. Just one such case is enough to make their statement accurate - I don't think he generalised those willing to die, but those unwilling to accept that as their choice. Based exclusively on my experience, that is a valid generalisation.

And yes, plenty of people have setup advanced directives, DnR's, and other such instructions while fully on their capacities, and that doesn't require them being in a pathological or even emotional state. It can easily be caused by having a standard of quality of life they intend to maintain.