I strongly disagree.
Despite not following the process by the book, I think it is clear that he attempted to act in good faith and had trouble with language/cultural issues. It's not like he posted porn or something on Zuckerberg's profile.
I think that going out of their way to stiff this guy out of a few bucks makes it all the more likely that any future vulnerabilities that are discovered by foreigners will just be sold to spammers/hackers. And this makes the internet a worse place.
Facebook saved a few bucks but just lost a big PR war here that Facebook will reward you for disclosing vulnerabilities.
Facebook should have paid the guy and used this event as a reminder about the best practices and procedures to follow.