Its 4 total, but its just two for each person. So imagine you’re following someones transactions onchain. You see them spend an to a single output. And then a while later they spend that to another output. Looks like maybe they bought something or more likely, they were just shuffling money between wallets. Unbeknownst to you, they no longer control those funds. Their funds are in a completely unrelated utxo.

Cool thing is it’s indistinguishable from a normal tx. Doesnt stand out the way a coinjoin does. It just literally looks like a normal tx.

So that means any normal tx could be a coinswap. You have no way to know.