Earlier quoted context omitted.
In his first message, he demonstrates that his bug exists by showing that he exploited somebody elses account. This is obviously , never the way to make a bug report. Heck, it's probably even illegal. You shouldn't need to read a sites terms and conditions to know that doing this will be breaking them. It's an expensive lesson. Hopefully it will lead to him being more sensible in future. I have no sympathy.
Denying bounty to a hacker on some bullshit "Terms of Service" violation excuse defeats the whole purpose of the bounty program. Next time a hacker will just sell the exploit to somebody else, cash upfront, and wont bother reporting.
There was no bait and switch - it's very explicitly stated that he should not be exploiting the vulnerability, and that it needs to be clearly explained.
I respect that he found a vulnerability, but he still needs to adhere to a website's terms and conditions. If the security team he reports a bug to doesn't "get it" the first time he should try again, not publicize it on Hacker News and attract negative publicity by putting it on Mark Zuckerberg's wall.