@Cynthia_Lau Hi, never seen this message before and not sure here. But I'm replying to "pick up the question" so to speak, someone will probably add to it. But ask the other org. if your account is still in their tenant (and a member of a private channel.) Have them remove you.
Out of curiosity, how does it look when going here?
There's a lot of caching happening in Teams, both on the frontend and the backend, so what you are experiencing might simply be because of stale cache. An easy way to check is to open a new private browser session and see if the entry still appears, but as long as you dont see this organization anymore under your Azure AD profile, it will eventually disappear from the client as well.