I was thinking more along the lines of your second sentence. When 9/11 happened he was probably old enough to really see things that he couldn't quite see when he was younger. During the Bicentennial in 1976 (I was 8) the world was a great place where nothing bad really happened. When the Iranians took the embassy workers hostage in 1979 the world the world was a much different place. It was the same world but I had learned to be aware of so much more.

Of course being front and center for so long the media really highlighted all the bad things in 1979 so I was even more aware of them then I probably would have been otherwise. The same thing happened for a while after 9/11 so your brother-in-law might not even really be aware that helped him see things differently.