Note that Secret Chats in Telegram is the only way to fully encrypt your messages without revealing their contents to the Telegram company. Moreover, Secret Chats are not available for bot communication.
And since we can't verify that ''full encryption'' we have to trust that telegram is doing what they say they are doing, and this excludes bugs and flaws in code.
I also think that secret chats are only available for smartphones, not for telegram app installed on computers.