Yes, the distinction between theory and hypothesis can be important, but a distinction should also be made between popular science and rigorous peer-reviewed literature. Popular science is meant to be easy for the general reader to understand. Often that means using simpler words, as long as they are still accurate in a general way.

In this case, I believe theory is an acceptable word to use. The MW dictionary, for the definition of 'theory', says

2a. "a belief, policy, or procedure proposed or followed as the basis of action"

3a. "a hypothesis assumed for the sake of argument or investigation"

Seems to me that the usage in the article fits either of these definitions well enough.