The word "lifestyle", as with any word, if used a certain way, can convey different messages or meanings.
One couple I know constantly refer to polyamory as a "lifestyle", meaning that they have chosen to be polyamorous. While I do believe, as a couple, there are choices to be made about polyamory, that for me personally, being polyamorous is not a choice or a lifestyle decision, it's just who I am. I don't think gay people have chosen being gay as their "lifestyle".
Polyamory was never a lifestyle choice for Ann & I. Early on, during the difficult transition from monogamy to polyamory, we would argue and challenge each other to return to monogamy. This was a non-starter and was never really a choice for us. So, at the end of it all, I guess we chose polyamory together but never considered it our lifestyle. Its just who we are.
Me: Late 30's male. Ann: My wife. Minnie: My girlfriend and Ann's best friend. Jeff: Ann's boyfriend. Shawn: Minnie's other boyfriend. Christie: Jeff's wife.