Exactly. To quote the Police spokesman; "He kept maintaining it was a clock, but there was no broader explanation" and "The concern was, what was this thing built for?"
Why shouldn't he make his own clock?! Why does there need to be a 'broader explanation'? How can one develop an interest in anything if you must first provide an adequate explanation? sigh
Why are you trying to teach me English? This teacher should be arrested for trying to overthrow the government... What is the "broader explanation" for this English textbook?
And those guys learning to fly the planes without the landing, why can't that just be an interest! With terrorism, if you want to avoid false negatives, you are going to have a lot of false positives.
NB I totally agree it would be a douche move to charge this kid with some BS, but investigating unusual behavior is much more understandable.