someone shows up with a Lit degree but still knows how to code and program
Now you're adding additional qualifications. I've known some excellent programmers who had degrees that weren't in CS or a related field. In that case though their degree is irrelevant. Why not hire people who have on HS diplomas? I've know some excellent people like that too.
I know a couple of Google employees without bachelor's degrees. One has an associate's degree and the other didn't even complete high school. Both are brilliant people and outstanding engineers. Google doesn't really pay attention to credentials in the interview and hiring process. Bock's point wasn't that the CS graduate was more likely to get hired because of what would be written on the diploma, but because the more challenging coursework would be a better preparation.
This presumes, of course, that the CS degree program really is more challenging and requires more critical thinking ability than the English program. I'd generally expect that to be true, but there are counterexamples. My university, for example, had such a weak CS program that the English degree probably was harder.
I should point out, though, that most Google engineers do have BS or MS degrees, along with a substantial leavening of PhDs, and most of them are in CS, math or other engineering fields, but far from all.