This 18 year old kid's actions made an enormous difference for good in the security of _every single user of GitHub_.
And for that, he gets banned. WTF.
GitHub needs to man up, say thank you, publicly apologize for banning the kid, and politely ask people in the future to send Rails exploits on GitHub to some.email@account they've set up to ensure they're dealt with promptly.
Claiming the "letter of the law" here is making GitHub look seriously petty and lame.