[null and void]

Was the bill actually counterfeit?

A spritz with spray starch can make any bank note fail the counterfeit pen test.

[arthurus]

One cannot know that this was determined from the article. Only the US Treasury can determine whether it is truly forged if it is a good forgery. That pen tells the clerk that he doesn't want to take the bill, that it is probably a forgery. Now if it was a Xerox $ten then the kid is out of luck.