That is because the item was shipped 1st class international, which is not trackable. As mentioned above, USPS trackable shipping (priority intl) starts at three times as much.The weight of 68 gr. is perfectly appropriate for a watch movement in a padded envelope.
Depending on the country, provenience and other factors, there is no invasive scanning of small packets, often more frequent is the use of sniffer dogs for drugs. However it is always possible that packages are inspected and value re-assessed by customs.