The prof mentioned that if both parents were brown eyed, their children would be brown eyed.Except this is not necessarily true. Using the simplistic model, the blue gene is recessive. So both parents could have brown eyes, but both have a recessive blue gene. The child could then get the blue gene from each parent and have blue eyes. So it doesn't prove the kid was adopted.
I think it must have been reversed. Maybe she had brown eyes and the parents both had blue eyes. I don't know how this article affects that process, but to my knowledge, there is no way for 2 blue eyed parents to have a brown eyed child.