Mostly because it isn't anything, really. In the course of a few hundred words, Terry complains about the storytelling, calls it funny, claims that only people who don't know what SF is call it SF, is scared by it enough to hide behind the sofa, and watches it every week. There's not a point there, not an essay with a thesis or a proclamation. It's just a comment on Terry liking the show despite being a bit hung up on its irreality.
(And Terry's wrong about it being SF -- SF includes, and always has, more than the merely plausible. Yes, at the Doctor Who end of things, the only difference between SF and fantasy is whether you're calling it a magic wand or a sonic screwdriver, but the trappings do matter.)