"when a member sends a group message, it essentially sends a one-to-one message to the other members. Therefore, the encryption security of small groups is almost equivalent to that of one-to-one chats, but the number of members it can support is limited."

Because of this, some Nostr clients seem to have trouble distinguishing whether a message delivered to me is from a small group chat or a 1-to-1 DM. I've been switching between so many different clients that I've forgotten which ones they were.