I think Hank realized he may have overplayed it a bit once Walt went into Heisenberg mode. He doesn't have anything yet and just tipped off a guy he always believed to be very dangerous. He had put the pieces together but until that last moment in the garage he had never truly connected the man in front of him, his friend, to the monster he was looking for
what a great scene though. They seemed to really nail it and kudos to the writers for giving us that in the first episode. I figured they would draw it out a bit