Definiely interesting. But I think the evidence is getting clear that almost any kind of activity changes your brain. I've seen similar research related to knitting and learning foreign languages (two other areas of interest to me), and I don't doubt that the same applies to playing sports, cooking, playing games, and a host of other activities. After all, isn't that what we teachers are trying to do every day in the classroom? It's long been known (if not always expressed well) that learning math, for example, isn't just for solving problems on a piece of paper, but it helps develop mental skills for solving other kinds of problems as well; learning science can help us to learn to anaylze all kinds of information to sort the true from the false. I don't doubt that all of this changes your brain, in a similar way that exercise can change your body by developing certain muscles.
And yes, birding doesn't mean we are more observant in other areas, but it may help us to be able to more quickly develop that observation skill in other areas if we want to. Note that the medical students still had to go to med school, not just go birding!