Yes, but the point is, if those people don't use ecryption, then they have a problem anyway - and if they do, but their system is compromised, than the attacker gets anything anyway.
In either case, I think Signal's job is to secure the messages going out and coming in and not protecting the disk.
That is Moxie's main point, full disk encryption should be used everywhere, and encrypting Signal's message database on Android is purely due to full disk encryption on Android being a steaming pile or bricking your phone.
