Basically, Mark Cuban talked to some people in the school (though he does mention it's twice removed so it is basically rumous) that Ahmed brougth it to five classes and the sixth one was the english teacher, and that he didn't engage with the teacher or provide any explanation what the device was.
My guess is, since the kid has never been in trouble before, he got very nervous when the clock got him in trouble. I know, when I was that age and being very shy to boot, being keel-hauled by a bunch of authority figures would have freaked me out.
Personally, I think the engineering teacher screwed up when he told the kid to keep it to himself. He should have confiscated the clock and told the kid to pick it from him at the end of the day. Then, none of this would have happened.