As soon as the guy's head hit the cement, he ceased resisting. I'd say it was a successful maneuver. And no, I don't think he hit too hard. The man was still conscious afterwards, and wasn't blinking excessively or looking everywhere with confusion... and hell, he didn't even cry out (which most people will do when they think they've cracked their damned skull or done some other serious injury). Someone else mentioned the sound... which on concrete is a very distinctive, hollow sounding 'Thod.' An arm and hand took most of it, by the look and sound. Lucky him.
I think the perp just realized he'd had enough resisting, and didn't want to go through THAT again.
Life begins & ends cold, naked & covered in crap.