It looks more like a bomb than a clock, to me. In fact, even if it does not look like a bomb, it still does not look like a clock.
That's just what it looks like to me.
I don't think he intended on scaring anyone, but the way it looks, of course the teacher would be scared.
Better safe than sorry.
The teacher did the right thing, because, if it had been a bomb, and the teacher did nothing, the teacher would be at fault for not saying anything. This was not a case of prejudice against any particular race or religion. It was just the teacher being safe. If you think there is suspicious activity going on, always report it, even if it may be nothing. Because, you never know if it is something. That's what the teacher correctly thought.
What confuses me about this issue is the fact that the student called the clock an "invention," and we already had the clock, even during George Washington's time. So, that's not an "invention."