Don't think he was at fault at all for the first goal, their player had beaten both Lynch and Butters then hit a hard low cross across the goal, with their forward rushing in with Hart in pursuit Henderson tried to cover his near post by knocking it away from the goal which he did but only straight to the feet of the onrushing Hart who bundled the ball into his own net.
As a keeper myself knocking the ball to the side is something you instinctively always try to do but isn't always possible because there are times you are just trying to block something irrespective of where it is going after, on those occasions you need your defenders to help you clear.
Personally I prefer Henderson, he will improve, Kuipers was a great shot stopper but could at times go walkabout with crosses and his kicking was a weakness.