When you first enter F3 key in the Vendor card to create a new vendor, Navision will create a Contact for this vendor automatically. This contact will have the same name and addresses with the vendor card. This happens automatically without you knowing it.
When you enter a name at the Contact field, Navision will create another contact for this vendor in the Contact table. As a new result, this Vendor will have 2 related contacts in the Contact table if you enter a contact name at the Contact field in Vendor card.