When a contact's property history shows Analytics as the change source, it usually indicates the contact was created through a non-HubSpot form on a non-HubSpot hosted page.
In some cases, this is due to JavaScript events that work with the HubSpot Tracking Code to create a contact in HubSpot when a visitor's email address is detected on the page. This can happen when a visitor enters an email address in an email field on a non-HubSpot form on a page that uses the WordPress plugin or is set up with the Events JavaScript API.
Learn more about the various change sources that can be found in a contact property's history.