But why not just "happened"?
Or not "has happened" in case of fresh news.
I can't see why a continuous action, a process of happening should be underlined here.
In my view it is either:
1. Present continuous if the speaker doesn't care whether the news is about yesterday's event. They are news in general. He is reading the freshest newspaper. So, for everybody this is the actual news. So,they are about current situation in the world. As current as possible technologically.
2. Present perfect as the news he is reading about is fresh and influence current decisions. Suppose he is a stock ecxhange speculator reading Financial times. What he is reading definitely influences his immediate actions. As this is the most actual information. A new law has just been published. Isn't it a subject for Present perfect?
3. Past simple. He considers tne news as a history now. Events happened and gone.
I can't imagine Past continuous here.
By the way the textbook is old. There were no Internet at that time. Or even if it existed, it was not the main source of information.