If you chat with one user from Matrix.org or one user in your room is Matrix.org (or any org they host for) then all of that chat data will be synced with them. A room with any general traction will inevitably have someone from Matrix.org & there’s not a lot of options to choose from (I’ve seen a lot of instances shutdown because of the cost to sync all that data was too much).

But that’s why I said “in practice”.