The real concern here is whether this was done as a social experiment, or some kind of test of equality or racial discrimination, to see what kind of response would occur if something "shady looking" was brought to school. I haven't found any pictures of the actual device, but it was in one of those metal pencil cases that looks like a briefcase with a handle, and it had a steel cable around it. About half way through the video the boy says "I closed it with a cable because I didn't want to lock it to make it seem like a threat so I used a simple cable so it wouldn't look that much suspicious". The very fact that the boy admitted to the fact that he himself had concerns about exactly how suspicious it appeared gives me the impression that he (and / or his parents or whomever) were trying to walk the finest line possible on making this benign from a legal standpoint (it wasn't locked, and wasn't dangerous at the end of the day), but still raise questions and some amount of suspicion as to what all may be inside.
It sounds like that is what the police are considering - was done to "test" the response of schools and police by walking that thin line between innocence and baiting.
A far, far more extreme example would be to have 9th graders of various races point a fake gun at police offices to see which ones get shot. Of course that is taking the example to the extreme, but I'm curious if that was the kind of thing that this "clock" was about. However, since pictures of the exact thing he brought to school are not available, none of us can even form an opinion for ourselves "does this look like something that a reasonable person would be concerned about in this context".
And finally, I want to point out that taking a clock's innards out of its original plastic case, and sticking it in some other enclosure, is not "inventing" or "making". It's cool stuff and educational (I loved taking things like that apart as a kid), but it's not actually making a clock.