Just because an event shows up in the Google Calendar app doesn't mean it's syncing to your Google Calendar account in the cloud. Google Calendar will also display events saved to the local Phone account (and presumably the Samsung account as well). These accounts don't sync to the Google Calendar account. In order to get them into your Google Calendar account in the cloud, you'd have to export the calendar to a .ical file, then import it to your Google Calendar:
https://support.google.com/calendar/answer/37118?hl=en