I do think that I have a polyamorous nature, and that I'm not inclined toward monogamy. This wasn't always the case. I've changed. After my first love relationship crumbled, something fundamentally shifted in my heart and soul. I'll never again expect that any single person or relationship can fulfill all of my needs for intmacy and loving. So far as I can tell. And that is in no way suggestive that I can't love fully. I can.
I'm capable of monogamy. It's just not my preference. Is it an orientation more than a preference? I suppose it is. Hmm.
So, yeah, I think I'm a poly person. And I'm not sure it matters so much that we all agree on how to use language to define or describe our relationships. That is, if there is a poly person and a mono person together in a relationship, I'd say let them decide whether the relationship is poly or whatever. For some, it will be important to define the relationship as poly. Great! Let 'em. Others won't define it that way because some member/s of the grouping are mono. Fine. Whatever.
I'm willing to be persuaded that I'm missing some important point in my response. I'm just trying to find the most respectful approach to the question -- and, frankly, I'm not sure it matters much how folks settle it.
One thing does seem clear enough to me, however. Some people are poly -- whether or not they are involved in "romantic" relationships and whether or not they have multiple partners. I'm definitely poly, but I have only one partner! At the moment.