In your case there was no proof of wrongdoing and you were not punished. You shouldn't see that as a failure to apply a "beyond reasonable doubt" or other standard of proof. It's a success, the system worked. Generally speaking there should not be a standard of proof for students to even raise concerns, because if there were then students would be unable to get help establishing the evidence when they genuinely have been wronged. At this stage of proceedings it's an inquisitorial not an adversarial system. Even in a serious case that moves to an adversarial venue, the student is not the prosecuting attorney and isn't responsible for proving the case.