If the et/open ruleset is not enabled, there should be no reference tho them in the output suricata.rules. The only time this is not true is when no ruleset is enabled, then suricata-update uses et/open by default.
The extra rules you are seeing are likely the engine provided rules like tls-events.rules, dns-events.rules. These are included by default as well, and aren’t really considered a ruleset you can enable or disable. You can disable them using disable.conf though.