Not true! Swingers and some other open relationships are not polyamorous because their connections are about sex and only that, even if they are friendly to and even care about their partners. The primary relationship is still the core and if one partner fell in love with someone it would cause problems. Poly (many) amory (loves) literally means multiple loving connections and although it has all sorts of configurations may well include no core, primary relationship. Falling in love with someone else is not an issue.