"End to end encryption" can mean either a scheme in which each device has its own key and arranges to trust others, or a scheme in which a key is shared across

"End to end encryption" can mean either a scheme in which each device has its own key and arranges to trust others, or a scheme in which a key is shared across devices (symmetric). Just because there is only one key doesn't disqualify the solution from e2ee status. If the middleman does not have the key, it's still end to end secure.