I will be so sad if it's as bad as Whatsapp in privacy department :(
From here https://telegram.org/faq#q-how-are-secret-chats-different
""" Q: Why not just make all chats ‘secret’? All Telegram messages are always securely encrypted. Messages in Secret Chats use client-client encryption, while Cloud Chats use client-server/server-client encryption and are stored encrypted in the Telegram Cloud (more here). This enables your cloud messages to be both secure and immediately accessible from any of your devices – even if you lose your device altogether. """
They claim that it's encrypted, but that uses a different kind of encryption.
Maybe this has changed recently?
The quality of the text is btw very questionable and dubious as e2e encryption has nothing todo with where the message is stored. See email where your gpg encrypted message is stored on a lot of systems on its way to reach its final destination. This text makes me distrust Telegram even more, thank you for sharing this!