Reading? What the…?

Dexter can read some words. I'm not sure exactly how it happened. We proved it when we were reading a new book and he very clearly read "good night" on the page. It was a new book, so we didn't think he had it memorized. We tested him with other pages. Sure enough, he just told us what color the words were. We turned the pages back to the "good night" page and he very clearly says "good night." How weird is that?