Encryption doesn't have to be backdoord because none of the group chats on telegram are encrypted (telegram gets to claim it's "encrypted" because it's TLS between client and server, but e2ee is not claimed except for inconvenient device-to-device chat.
In any case, the back door may be more of a Room 641A arrangement where all messages are intercepted by the host government, saving them the trouble of installing sockpuppet accounts in all the chatrooms they want to keep an eye on
O no you're right, I was going off the fact that it's just an encrypted tunnel from client to server, doesn't hide any message content from service provider the way people might expect when they hear "encrypted"
The cynic in me believes that the motivation behind this very publicized melodramatic arrest is even simpler: reinforce the myth that Telegram is e2ee (remember the 90s when the DoJ wanted us to believe that 40bits keys were unbreakable?)
In any case, the back door may be more of a Room 641A arrangement where all messages are intercepted by the host government, saving them the trouble of installing sockpuppet accounts in all the chatrooms they want to keep an eye on