From the article:

Through a large-scale, random-assignment study of school tours to the museum, we were able to determine that strong causal relationships do in fact exist between arts education and a range of desirable outcomes.

Students who, by lottery, were selected to visit the museum on a field trip demonstrated stronger critical thinking skills, displayed higher levels of social tolerance, exhibited greater historical empathy and developed a taste for art museums and cultural institutions.

yay art!

Yes, yay for art without a doubt and nothing against it, but maybe these kids would have exhibited the same results if you simply took them to a bowling alley.

What was the baseline cohort by which the kids "...demonstrated stronger critical thinking skills, displayed higher levels of social tolerance, exhibited greater historical empathy..." and etc.  

I'd imagine it's not difficult to beat the baseline of kids that remained in boring classrooms and didn't have field trips.  

Was it really art that made all the difference or simply getting out and having a real experience with a group of peers once in awhile?

Art makes the difference by encouraging people to get out and have a real experience.