This is a good question and I have to agree with some of the answers given already, mainly those regarding being true to who we are and that well, this is a poly forum.
I don't know who, if anyone, has noticed that when I refer to myself as poly, I say that I have poly tendencies. Maybe this is because the only poly relationship that I have had never progressed to a fully sexual relationship. I would probably fall into the category of a poly person who could stay mono and be happy. Does that mean that I may never want to go down that road ever again, no. It just means that I do not have to be in more than one relationship to be happy. Hence, poly tendencies.
I suppose it could be equated to someone who has homosexual tendencies but doesn't feel they are either gay or bi. They could be with someone of the same gender but they don't have to to be true to themselves. I hope that makes sense and is not offending to anyone as I am neither gay or bi myself.