Nitter is an alternative front-end that allow you to view the tweet and the response while Twitter only only to view the attached tweet only. So in fact , it's better that he used nitter rather than the "original"
Twitter is not a publicly available resource, not part of the open web: Its URLs are semi-private and require an account to fully read and they should not be posted here on HN.
For almost two weeks they were fully locked, and now one can only see the original post and not the thread, and all browsing is locked out.