That has "military grade encryption" vibes.

Very secure but not investing in rolling out this mtproto they went through so much trouble to invent, nor making it usable by implementing device sync or all the other features normal chats have. Why does it smell like fish all of a sudden?

Except Pavel Durov has been caught lying before and in general is not a great source of information.

Very secure servers are openly documented (Kerckhoff's principle).

Snake oil purporting itself as secure is always very hush hush and comes with claims of security.

Besides, other messengers like Signal have already made the server open source, and they have native clients that end-to-end encrypt everything, so you don't even have to trust server.

Durov requiring you to trust the server shows he has no idea how to build secure systems. He and his team are amateurs in security engineering.