Yes it was a brilliant and revealing article, very scary as well!
However as Sam2 said, the number is extremely high because they are including ALL members of “Yeshiva High Schools” regardless of how that school defines Orthodoxy. Some of these “Orthodox” schools have a school sponsored prom, and many of the kids come from homes that are not keep Shabbos at all anyway. In that case the kids are not “off the derech”, rather simply following the “Derech” of their parents!
That being said, the real number is high enough his article was spot on about the issues and how to solve them