The Bureau of Customs is the agency that is responsible for enforcement of tariff on goods. In general all the goods that are imported into the country are subject to import taxes. However, some goods are duty and tax free such as goods imported for personal use. I believe you brought that note book with you for personal use. And thus the tax charged by the official was unnecessary. Here is a link that gives complete information about stuff taxation and duty laws in Argentina and the contacts of the concerned authorities.
www.fedex.com
www.fedex.com
