Given that HackerRank has more than 1000 employees, I agree that it is surprising that they were able to react and apologize on the same day as the takedown and all the buzz on social media.
However, I still think it's a damn shame that HackerRank needed such a high-profile incident before reconsidering their shady arrangement involving probably-automated DMCA takedowns against GitHub repositories. Either they didn't know what that would incur on open source repositories hosted on GitHub and other platforms, or they just didn't care about it as long as it wouldn't cause a huge fuss for themselves (which it did in this case).
However, I still think it's a damn shame that HackerRank needed such a high-profile incident before reconsidering their shady arrangement involving probably-automated DMCA takedowns against GitHub repositories. Either they didn't know what that would incur on open source repositories hosted on GitHub and other platforms, or they just didn't care about it as long as it wouldn't cause a huge fuss for themselves (which it did in this case).