Telegram isn't encrypting chats (only secret chats).
As far as reproducible builds telegram has got instructions and caveats or excuses around builds for the same issues signal does: https://core.telegram.org/reproducible-builds#reproducible-builds-for-ios
Both easily make Android reproducible builds. This Twitter message is a rock being thrown in a glass house, knowing most people who consume Twitter like it's a firehose, won't swallow the nuance of the details.
I don't even, not to complete lengths.
I've seen similar on my desktop on proton when on wake it crashes the display manager and shows my locked desktop unlocked with all the running applications before it finishes crashing closing all my applications and then going back to login screen.