Considering that the word "predict" or "prediction" doesn't appear anywhere in that page, you're wrong.
Tom. Ok. Let's try to break this down: Supernova were observed. In the middle of the 20th century a possible mechanism was proposed. That mechanism implied that supernova would also send off strong bursts of gamma radiation. That prediction has been observed in a few supernova since then. But you would likely assert that in those cases that NASA was involved in tainting the data. So here we have that same prediction- the burst of gamma radiation, verified by physicists using historical supernova.
And Tom, as to it not having the word "predict" there you might want to reread the paragraph that says "The gamma rays from nearby supernova ought to have a significant impact on our atmosphere, in particular by producing an excess of nitrogen oxide. This ought to have left its mark in the Earth?s ice history, so the team went looking for it in Antarctica." Saying X ought to happen is a prediction.