I was wondering about that earlier myself. However, Amish schoolhouse vs. Virginia Tech. is a bit of a different dynamic.
With the former, you've got (many) fewer pupils, so managing the situation and controlling the people would be easier.
With the latter, you've got adults, who are physically much larger and stronger, and there's more of them.
That said, I'm surprised to hear students actually lined up (if that's really what happened). You'd think everyone would scramble and panic or try to escape.
Yes, it’s different. But he could still have taken an idea and applied it to his own situation. If so, then he’d probably been planning this awhile.