Not exactly. Socket units can pull in services that are not otherwise enabled. You also have to search through all of your udev rules to check if there are SYSTEMD_WANTS directives pulling services in.
rav (correctly) said that enabled services are started automatically on boot. They didn't say that non-enabled services are not started automatically on boot.
You're right that there's a lot of nuance to the set up. I think listing that directory will solve the "it's 4:00 am and you want to know if nginx will start on boot" scenario, but you're right that you need to understand the system in more detail if you were to build tooling around it.
