On the live installer, the password entered for the disk encryption is so loose that one could even create a password of 1. The rules for creating the user's password are much stricter and I believe the rules should be the same between the two passwords.

This behavior was verified on https://downloads.puri.sm/live/gnome/2018-08-26/pureos-8.0-gnome-live_20180826-amd64.hybrid.iso