Of course, she had no way of knowing that he had the Force, that he could likely deflect anything long before it hit him. Luke decided it was best to be calm and try to find a non-violent resolution to things.
"I'm sorry...I don't mean any harm. I was just practicing my skills. I wasn't sure where the arrow came from. It's hard to notice things sometimes when I'm concentrating." he replied. "I don't like to fight, though, unless I have to."