I’m not sure they are lying. Yes, they’re not E2E but I don’t think they claim to be by default, do they?
I’ve got a large group of friends there, since high school. We presume everything we write is available to the Russians so we never talk work details or share secrets. It would be insane otherwise.
We’ve tried to organise a move to Signal, but honestly its client is nowhere near as polished or feature rich as Telegram.