From the article:
Puddie says he didn't initially tell anyone he had the pen because "I didn't want to get in trouble."
That's where he made his mistake. I would absolutely believe that he didn't realize it was an extremely valuable pen when he took it. But when he realized that the pen was valuable, he should have just taken his chances and told them, hey, it was sitting on a counter and I needed a pen. I didn't know that it was valuable.
Mike