It does surprise him, but not for long enough for it to make a difference. It only means that he rises a bit on his hind legs and she's hit by one of his front legs, catching her under the chest and hurling her off the rooftop.

A very observant onlooker might notice that she falls in a strange angle, as if she had a running start into nothingness, but he'll just hope that nobody will look or think that hard about it.