I just used the manjaro-arm-installer and build myself an rpi installation.
Mounting the sd-card before booting from it and pacman.conf includes following lines:
[core]
Include = /etc/pacman.d/mirrorlist
[extra]
Include = /etc/pacman.d/mirrorlist
[community]
Include = /etc/pacman.d/mirrorlist
Maybe the script needs to be updated somewhere?