But that doesn't mean the Doctor would've known. He was "born" in the DQ with a limited set of knowledge and expanded it selectively based on what he found interesting and useful to know. There could've been enormous gaps in his knowledge. Heck, we all have gaps in our knowledge compared to other people. For instance, I live in the United States, but I couldn't tell you much of anything about contemporary American pop music or sports, because I don't pay attention to those things.