The HN post title is incorrect. It's the exploit author who responded, not the hacker / cracker.
Ok, we edited the title to say that.
Pedantic correction: the hacker does not respond the author of software exploit tool responds. Firefart himself did not actually hack into the sysadmins server, he wrote the code for a PoC that exploited dirty cow vuln. It seems the hacker used this code to gain root because of the unpatched software
Reminds me to always update my servers. And to always install a FIM (File Integrity Monitor) on the system.