Short answer
HubSpot's KB: calendar sync only uses the user's primary calendar, and you can connect Google or Outlook, not both. Events created before you connect won't sync. Deleting a meeting in HubSpot doesn't remove the calendar event.
1. The setting
Calendar preferences in my demo portal, not connected.
2. Keep meetings out
To stop some meetings logging, see the never log list.
3. Related
Recurring meetings not logging.