Nature.com also covered this story, and similarly used the phrase 'Moon's origin resolved'. This would seem to confer a certain respectability on the assertion.
The problem of how the Moon could be so similar in composition to Earth, assuming the giant impact hypothesis, has long been a problem. It would seem that the impacting body, making up most of the Moon's substance would be more dissimilar to Earth than appears to be the case.
This new analysis appears to make this less improbable. If the impactor, called Theia, was Earth's smaller 'sister', formed at the same time, in the same region of the solar system, their resemblance to one another makes a certain sense. Link to Nature article, below:
http://www.nature.com/news/puzzle-of-moon-s-origin-resolved-1.17279