I consider them, and I'm sure you, to be polyamorous. It is a descriptive term. I will apply it descriptively to anyone who is
open to more than one "romantic" relationship at a time.
From a purely descriptive use of the term polyamory, I would have to concede
my open marriage is polyamorous.
However, it seems to me a waste of time to circuitously describe a concept which is described concisely by a now-largely-accepted single word because other people have decided that they get to say "polyamory is exactly X, Y, and Z."
People can go around all day saying that "Marriage is only a lifetime commitment between one man and one woman" or "Polyamory is only complete openness to all sexual and romantic relationships where the concept of jealousy is rejected" or anything else. The word is in common useage among non-poly people without all those caveats.
Just some thoughts... :-) Kelly