Evidence is submitted to a court. A cop is legally allowed to lie to you (but not your son), so I wouldn’t trust anything they showed me anyway. In other words, don’t sweat it that he didn’t ask for evidence and none was showed…. In fact, I’d unlearn that bad habit now before he goes much further in life thinking that requesting evidence is an important step.
Before you get to a judge you’ll probably stop by the clerks desk and get a plea agreement explained there. Plea in abeyance is what you’re shooting for… common terms are no moving violations in the next 3-6 mos and it comes off the record… pay a fine.