You would be right, but remember, the question explicitly is asking about Walt, and says he is indeed a member, and that all members must do one of the two ways. There may be other ways outside of the vacation club, but that is irrelevant.

I am thinking of it like this- there is either a world where tigers are not mammals, and this argument is wrong, or there is a world where tigers are mammals and the argument is right. It's one or the other. These things cannot simultaneously exist.

However, it is possible that we live in a world where tigers are both suitable and unsuitable pets (in some conditions, to some people, maybe a dangerous animal is okay- maybe they have a custom built enclosure, whatever..)

There's just more room for argument in the suitability question because it's technically an opinion. You could never really "prove" to anyone that a tiger is unsuitable as a pet, because what does unsuitable really mean?