During data import, there is some object export that is related to another object. The object relationship is only referenced using ID, hence, it’s impossible to identify the object type that it’s related to.
Here we would like to share the parameter you should use to know the object type that is related to Event. The following is a data export of event record.
To get the associated object:
From the above, you will see the event is related to the contact and campaign object.