if they can read the messages then its not strictly speaking e2ee
Yes, it can absolutely still be E2EE: the message is encrypted and the central server does not have the key. The issue is that the clients (i.e. the "E"s) are controlled by the same entity as the central server, and we don't know exactly what the client (app) is doing. So the fact that it's E2EE is somewhat moot.
This is exhibit #1 in the case for open-source software.
PS: you obviously get this, I'm just trying to make it clearer for anyone who doesn't.