This guy is so boring that a) we're glad he's only in one chapter of the book, and b) it's no wonder he doesn't have the imagination to grasp what actually happened to Sadie and Carter in the British Museum. Here's how Sadie describes him: "He wore a lint-colored suit that matched his gray hair and his ashen face" (3.40). He scowls a lot and has funny-looking eyebrows.
Oh, and he accuses Sadie of aiding her father in terrorist acts like blowing up the British Museum. He also lies to her, saying that Carter has already come clean. Sounds like a nice guy. Not. But he is a good example of what happens when magical acts extend into the mortal world, and people who don't know about gods and magicians scramble for rational explanations. This guy probably has a rational explanation for everything, so no wonder he gives Sadie and Carter such a hard time when their dad mysteriously goes missing.