With Mail Privacy Protection switched on, Apple Mail loads remote images through Apple’s relay servers, whether or not the message is ever opened. A tracker that counts every image request therefore shows opens that nobody made.
HawkOpen checks each image request against named rules. A request that matches the Apple rule gets the category privacy proxy and the rule code R-OPEN-APPLE, so you can see why it was classified that way. The category is an estimate; it does not tell you whether the person later read the message.
Mail Privacy Protection loads images, not links. A click on a tracked link is therefore not caused by it, although company security scanners can still click; HawkOpen rates every click with its own rules.