Looking at it again now, it really looks like Smith went in expecting to need a lot more force to get Robsinson to the ground, but when Mullen has driven him down himself Smith has more or less lost control of him and fallen on his head in an awkward way. I know everyone will laugh and say im reaching but that's really what it looked like. I really think he had his arm there with the expectation to make a big slamming tackle, when when Mullen beat him to it he lost control. I didnt see a second effort at all. Hardly what I'd call a head slam, but if the NRL are trying to cut everything out of the game then I'm not surprised he was sighted for it, especially given his reputation for the niggle.