He got shot with chewies blaster which was shown several times to knock people through the air. It was a surprise Ren was walking much less fighting. It's why it showed him pounding on it and blood falling. Plus he tried the whole "I can teach you" thing. He wasn't in his best fighting status.

Also, Ren is shown to naturally use the force rather than fighting it. She let's it guide her instead of fighting against her intuition. That was the point of how she figured out how to fly the falcon. After it was confirmed that it actually exists instead of "that's silly!" it was "well let me try it." Both Anakin and Luke also were force sensitive, Rey just let it lead her rather than thinking she couldn't or wasn't good enough to use it.