Sorry, I'm not entirely clear what you're seeing. Is the query driving the dashboard the "VSE: Threat count by severity" query, or a different one? Can you post a screenshot of what you're seeing?
As you wrote checkbox allow you to pervorm actions with table entries, for examle delete them. But if you need only log which are related to threats not handled you have to filter out them on dahboard you using. You can do this in query on which dashboard is based. This query has the same name as dashboard. In one of steps in query bulder you have filter option and you can put criterium