I would have been a complete wreck all day and all night if I were Walt, wondering if anyone looked at the computer already and even wondering if there's another recording somewhere. I think his cockiness is a defense mechanism. They can't really be sure if the hard drive was erased, but he needs something to put his mind at ease.
Also, Ted isn't dead. I didn't think he was when he hit his head, but everyone said he was, so I went with it.