Thane moved, just a bit, and still got hit. She was fast, of course, but she did sneak up on him, so he expected nothing less out of her. He'd be glad to enjoy spending a few moments learning from this fight, figuring out who she was. Her blow was hard enough to hurt, but not hard enough to make him falter (of course, he would have to be dying to stop). He didn't want to kill her necessarily, but her being alive put himself, Shepard, Garrus - and any of the others she was watching - at risk.

The capitol could be to blame for it.

He ducked down low, shifting his body to move and swipe one leg out to attempt to get them under her feet and knock her towards the ground.

He was testing the waters with her.