Ok, it does look like it's checking for list updates, just more often.l than I expected. I went into the settings and disabled as below and the calls stop. So all good!
"check update opt-in Check for update of version (on startup and when opening options): check update enabled: NO"
Many thanks for checking this. When I used the following setting in the extension I didn't see any further calls.
"check update opt-in Check for update of version (on startup and when opening options): check update enabled: NO"