To expand on Morons' answer a bit, the idea is that understanding the particulars of the code (syntax, and to a lesser extent, structure/layout) is easy enough that we build tools that can do it. Compilers can understand all that needs to be known about code in order to turn it into a functioning program/library. But a compiler can't actually solve the problems that programmers do.
You could take the argument one step further and say "but we do have programs that generate code", but the code it generates is based on some sort of input that is almost always hand-constructed.
So, whatever route you take to get to code: be it via some sort of configuration or other input that then produces code via a tool or if you're writing it from scratch, it's not the code that matters. It's the critical thinking of all the pieces that are required to get to that code which matter. In Linus' world that's largely data structures and relationships, though in other domains it may be other pieces. But in this context, Linus is just saying "I don't care if you can write code, I care that you can understand the things that will solve the problems I'm dealing with".