Telegram is known as a privacy-focused secure messaging app because it markets itself that way. However, it is often criticized by security experts, privacy advocates, and people with common sense who can understand why its claims about being privacy-friendly don't make sense. In this brief article, I'll show you all
I’ve no proof of this, but technically the whatsapp app is closed source so they could push an update that collects the private keys, if they don’t do this already
One way to prevent this is would be to re-sign the app with your own signing key and delete that key before court, I guess. But those people whose conversations appeared probably just had Google Drive plaintext backups enabled.