I was FF - and was a very well behaved obedient child.
My Dsis, 7 years younger and born by the time BFing was being encouraged in the 80's, was BF and was much much naughtier!
That said, my BF DD1 was held a lot as a small baby because she screamed blue murder otherwise - she lived in a sling for the first 10 weeks or so. She is very obedient, at present at least.
Did the study control for social-economic background, birth order and all the rest of it? If it is the "being held" that makes the difference, then you could argue that eldests are more obedient because mum only has them to deal with and has more time to hold them, whether they are BF or FF. Younger children have to fit in much more and perhaps get less "in arms" time.
Don't get me wrong, I loved BFing and thought it was great and will definitely try and do the same with DC2 when s/he comes along. But this study just doesn't quite add up to me.