I see their calendar status so I assume they see mine. How do I disable this function or confirm that it is not being shared?
If you do not share your calendar with the external user, he will not see your calendar.
There are two methods to share calendar. One is in Outlook client. Another is in Exchange/Office 365.
For more details about how to share an Outlook calendar with other people, please refer to this article:
About add/ remove calendar permissions in office 365/ Exchange, please read this article:
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