Cloudflare protects everybody who signs up, including control panels for "booter sites", which are web pages where you can allegedly buy a DDoS attack for an hourly rate.
Kind of like the police protects gangsters from getting shot by other gangsters, but you would really like them not to do that, so that the gangsters can just shoot each other.
In this case, Brian Krebs tried to convince Cloudflare to kick off the booter sites, so they are unprotected, and can DDoS each other. Cloudflare didn't put any effort into that idea, and now he's apparently angry that he didn't get through to them.