(Disclaimer: I'm not trying to bash poly people. Poly people are vaild af)

As a poly
That does somewhat happen occasionally

Different type

Wait

I'm Poly, We don't cheat. xD

It's a mutual understanding

When you're poly, You don't just hook up with someone thinking "Oh well, My other lover won't mind." xD

Yeah
From what I understand, doesn't everyone in the relationship agree that they're all together or something?

Yeah, Exactly.

As a mono person-

Fair 🤷🏼

If your poly you don't cheat you don't just hook up with everyone, for example, if you had only one partner at the time but wanted to date or engage in sexual activity with another person you need to make sure your partner knows and is comfortable with this and so is the other person.

Nahh that's more or less an open relationship. (Still valid, but a different type of ethical non-monogamy.) Polyam relationships can still be closed.

(Also it doesn't count as cheating if your partner said you were allowed to do it, lol)