You cannot say "it is not correct" without proof. We know all messages not just E2EE are wrapped in encryption on their way out a Telegram client and we know they are decrypted on their way in because client source code is available.
Why don't you have a look for yourself then let us know if you've confirmed your suppositions?
At this point you are just willfully throwing around misinformation. A number of commenters have tried to point you directly to the docs to which you've just said, "it's wrong".
> talking about MTproto, which is only used for their e2e chats.
This is also misinformation. [1] Please stop.
I only flag as an absolute last resort here on HN but you are actively harming discourse at this point.
[1] https://core.telegram.org/mtproto/AJiEAwIYFoAsBGJBjZwYoQIwFM...