This tutorial is outdated. We're not using the system-provided dnsmasq since over one year by now. Instead, we ship our own DNS server (pihole-FTL) which is a customized version of dnsmasq with lots of Pi-hole additions. This command is wrong:
sudo systemctl restart dnsmasq.service
Instead, try
sudo systemctl stop dnsmasq.service
sudo systemctl restart pihole-FTL.service