It's painful to read. Only one person in that thread appears to know what SELinux actually does, and nobody has mentioned the fact that SELinux was explicitly designed to make a root privesc contained.

The ironic part is that since DirtyCOW is a kernel bug they could probably modify the exploit to disable SELinux from inside the kernel (or load a module that disables SELinux). But they're just trying to use the PoC as the only thing you can get from the exploit.