Hi @jfb - no worries.
The issue I can see is that, as this is a service that is started via update-rc.d a normal 'disable' does not work as it leaves the various run level files hanging around as seen by ls -l /etc/rc?.d/*dns*
To remove those you need to execute update-rc.d -f dnsmasq remove.
Secondly, disabling a service simply stops it from running at boot, but does leave open the possibility of it being initiated by another service. To stop the possibility of that happening, a
systemctl mask dnsmasq.service
is required.
This then removes it from the output of a systemctl status and avoids confusion.
Thanks for your help.