Default Customer is a setting in WooCommerce Advanced. If you don't import a Customer or the system doesn't find a match, the Default Customer is assigned to imported Orders.
You might create a Customer you call WooCommerce Orders for this purpose.
Within an Order you can import all contact information, so it is possible to use one Customer card for all WooCommerce orders. Or, use it to catch errors where a customer is not found and manually correct any Orders set to the Default Customer.