If you had taken the time to read the original article, you will have noticed that the man in question is a German security researcher who designed his own malicious app to extract the contents of the 'keychain'. This is not the actions of a 'Mac user looking for a little side project' but the actions of someone specifically going out of their way to find something, in this case, software bugs in macOS.
He put his time and effort into finding the bug, designing his own app to exploit the bug all whilst knowing full well there is no bug bounty that would financially reimburse him for his efforts, but he carried on anyway. This therefore implies his intentions where not honorable and thus this was proven when he said he would not release his research to Apple until they introduce a bug bounty for macOS.
It's blackmail, pure and simple.