Per Googling site:telegraph.co.uk "by sir martin rees", Rees has written one piece for the Telegraph before, in 2013. He doesn't seem to write for other news outlets (although he has written a book), and if he has any background as a journalist, Wikipedia doesn't mention it. Calling him a "reporter" seems quite silly.
My friends invite me to dinner sometimes. They make the meal. That does not make them chefs, or cooks by profession. At best we can say they cooked that particular meal.
Being a journalist or reporter by profession is one thing. Saying that someone who wrote a single news article is a reporter seems to be an abusive usage of the word. At best we could say that he reported that particular event.
https://en.wikipedia.org/wiki/Martin_Rees