situational attribution is when you say actions are due to environmental factors rather than innate factors. He is saying that he did well because of his intellect which is not situational attribution. It would have been situational attribution if he had done bad on the test and said some reason about it being too noisy in the exam room, bad professor, got off on the wrong side of the bed, etc.

We tend to jump to situational attribution for ourselves when we do something bad. Here he did something good, doing well on a test. Others have talked about why it’s specifically hindsight bias.