When in doubt, always disclose. This incident is not a ... out and you didn't disclose it in the first place ... you don't need to disclose but generally schools will appreciate ...
Also, is it possible to randomly find it on a Google search? If so I would disclose everywhere. Just because a background check might not be international doesn't mean that this couldn't easily turn up elsewhere given the nature of the Internet.
I'm amazed at how many people don't read the instructions on their ticket. My center turned away several people because they didn't have pictures on their ticket and numerous people had grocery bags instead of ziplocs