It’s called a pseudopupil. It’s the part of the compound eye that’s collinear with your line of sight. As you said, the light is absorbed there and registered by the dragonfly. The surface of the rest of the eye is at an angle and reflects light from the surrounding, which makes it look brighter.
Enough for what? Your sense of vengeance? I don’t know, only you can tell… Enough for rehabilitation? I don’t know, but it is possible. Time needed for rehabilitation varies widely. It’s quite possible the year was enough. One thing we do know is that the Netherlands is heavily in favour of rehabilitation over punishment, since rehabilitation actually forwards society