In the Advanced Search criteria on Events:
add an additional row: use mode NOT,
and then for criteria use the criteria option on the left, choose the is one of operator in the data criteria wizard,
and then for Value(s) add all contact types, which should be at least 2 (main contact and other contact) but probably more also.
Then the results should only include the records where the event is on the candidate record specifically and ignore ones where the event is only on a contact record's events.