The BBC article is perhaps truer to the paper:

  Erik Wing, who led this research at Baycrest Academy for Research and Education in Toronto, Canada, compared MRI brain scans from bird experts to those of novices while they identified birds. He found that expert brains were wired differently in regions important for functions like attention, visual perception and visual recognition. 

"He found that expert brains were wired differently in regions important for functions like attention, visual perception and visual recognition."

Can we be sure that happened because of the bird watching, or did they reach expert level because their brain is wired differently?

Nominative determinism strikes again.

I agree, it would be interesting to see if there are some cognitive advantages associated with the "special interests" personality traits, in general.