GitHub Account hijack through broken link in developer.twitter.com
hackerone.com
hackerone.com
Might as well say that this bounty hunter got scammed and was rewarded with a pat on the back for 'great effort'.
At the end of the day, they had a hyperlink to an external site (GitHub) which they didn't control. Even if the link went to an official Twitter GitHub account, there is no guarantee GitHub doesn't change its URL structure tomorrow causing that bug again.
At the end of the day, when website A links to website B, at least some responsibility goes to the user to check they are where they intend to be.
I would. A researcher who may do this for a living did not get paid for valid work they did. By definition that is a scam. And it flys in the face of what a bug bounty program is supposed to insentivise. Every unpaid report is a signal to not submit other valid bugs, undermining the whole program.