A quicker alternative:

  comm -1 -2 <(pacman -Qq | sort) <(curl -s https://gist.githubusercontent.com/quantenProjects/3f768dce7331618310f016d975bf8547/raw/beef579f8a8efeed6ccf60788e5b768775550095/packages | sort)

It's never a bad time to learn about comm(1).