It is VERY LIKELY that a former or current SCO employee or someone who had access to the codebase simply added the code in. Why is that so hard for you people to believe? There are no controls in place to prevent it.
What are you talking about? You think there is public commit access to the Linux repository or something? You may want to check again on that.

Every bit of code that is committed to the official Linux kernel goes either through Linus himself, or one of many "lieutenants" who clean up/verify the patches, and then send them on to Linus. It is the same process by which FreeBSD development is done, except there are more people with commit in the BSD project. Yet Linux's development model is flawed somehow?