Could be wrong, but the product link is the link you make on your website, and "Other clicks" comes from the visitor browsing Amazon after they clicked on your link to reach the Amazon website.
Product Clicks - Readers are sent to this certain product from your website - banner, image, direct product link. Other clicks - Is where Amazon rocks. Like you promote iPhones but someone buys a camera, even though you don't promote it, you'll get paid. This is a good sign that your visitors like buying on Amazon, so try to make them enter Amazon more often - even if they buy something else. They have 24hours to order or you don't get money.