This is a real issue, and could have affected the security of real users, but I wouldn't fault Twitter for not rewarding this.

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.