This would be the same case for Telegram as well, if someone has your phone. I believe that Signal can have a lock on the client, and the database is encrypted.
The other part that Du Rove conveniently left out: Signal went against the US courts and won [0]. When subpoenaed to give all user information they gave them all that had: the unix timestamp of when the account was created, and the last date you connected to the signal service. That was in late 2021. I'm really curious as to what Telegram has told the FSB.
[0]: https://signal.org/bigbrother/cd-california-grand-jury/