"So it's this vulgar talking weasel and nobody knows they exist?" Kevin asked, mostly rhetorically. He didn't doubt Oriel (well, not any more than he doubted anything in the Quibbler, anyway), he was just still a little surprised Hogwarts' professors wouldn't have mentioned them at any point in their seven years.
Kevin was a Ravenclaw through-and-through. He got frustrated when there was something he didn't have even a hint of knowledge about, and he trusted his professors to know everything about their chosen subjects. If Hagrid had truly not known about these profane rodents, it represented a breach of that trust, even if it was an irrational trust to begin with.
He shook his head to try and dismiss the betrayal. "You just write up a bit about what they are and what they do?" he asked. "Not bad for a fresh-out-of-Hogwarts kid, huh?"