It is based on watchers or added to cart for over 5 days. You can watch an item without viewing it using the heart icon on a list of items in a search.
Also views now will drop off after 30 days. If an item starts with 1 watcher and 1 view and 30 days pass with no new ones, the view will drop off but the watcher will remain, leaving you with 0 views and 1 watcher. I hope that makes sense.
