Oh, I agree that lying to your partner is extremely damaging. My point was just that all of the things you listed were about doing stuff with the other person instead of with your partner or otherwise to the detriment of your partner (ignoring their needs, taking time away from them, etc). And while it's certainly possible an affair could work like that, the whole idea of poly is that you can have more than one relationship without them being detrimental to each other. So, couching an affair solely in terms of things it takes away from your relationship is somewhat anti-poly, I think.
Like, your connection and time with your partner might not suffer at all, you could be conducting an affair during the time you'd normally spend playing online games. It would still be an affair because it was a secret and the lying would still be damaging. But I don't think that any other aspect of it needs to be damaging or detrimental to your relationship in order for it to be classified as an affair, if you see what I'm saying.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.