An event is something that happens.
A risk event is something that is uncertain and matters — matters in the sense that it results in losses to the achievement of objectives.
Similarly, an opportunity event is something that is uncertain and matters — matters in the sense that it results in benefits to the achievement of objectives.
Can the same event trigger a risk event and an opportunity at the same time? You bet. Think about storm impacts on retailers and manufacturers of storm equipment. Block chain technology and other new technology advances often create cyber security risk events and business opportunities simultaneously.