AFAIK telegram has channels and groups which were used in russia for purposes the govt didn't want to encourage. To my understanding, both groups and channels cannot be encrypted, so this ban has less to do with encryption but with the fact that Telegram wasn't willing to handle over the plain text chats they have on their servers.
They certainly are encrypted, they're not end to end encrypted so Telegram has the keys. Supposedly each key is stored across multiple datacenters in different legal jurisdictions so no single government can compel them to hand over the keys, but this seems like a rather questionable legal theory.
