I am surprised by the attitude against what he did, both on reddit and even more so here. Afterall this is "hacker news" and the submission is called "hack your way...". Any definition of hacking that I know includes cleverly exploiting the limitations and boundary cases of a system. I see this attitude as part of a larger trend of "sandbox"-ification, "theme park"-ization of computing.
It is against the rules (and against common etiquette) to DOS the machine in CTF events. I don't see how fork bombing the machine helped him solve any challenges so I can't see how someone could approve to that.
And another way of looking at it is: someone offered you free entertainment and education and you slapped them in the face and ruined the fun for everyone for quite some time. "Hacker" certainly does not include or entitle you to being a dick.