The professors said the student was told by the agents that the book is on a "watch list," and that his background, which included significant time abroad, triggered them to investigate the student further.
It appears that it is not the fact that he requested the book that triggered the visit but the fact he requested it coupled with the time spent abroad. Sounds pretty reasonable to me.
There are so many people that have FBI files on them it is pretty standard procedure. I know I have on for the simple fact I own a firearm and have a concealed carry permit.