Comment by EGreg

The reproducible build of Telegram lets you evaluate the code doing end-to-end encryption. Once you satisfy yourself it's doing this kind of encryption without implementation-level backdoors, then you don't need to worry about servers reading it (except for #5 above).

I didn't claim it encrypted "group chats". I said "things". If you want me to be specific, the "things" are individual 1-1 end-to-end encrypted chats.