Johnny should have pulled the trigger, but he was admittedly a little taken by surprise that a woman not wearing anything would be bold enough to step into a gun. She also didn't seem as alarmed as he had imagined somebody should be.
He was ready to answer her in some smartass way, until she touched him. His mind fogged over and he found that he didn't really want to have his gun out anymore.
There was no holster on him, though, and Johnny wasn't the sort to tuck guns into his waistband. So he just held the gun to his side, automatically resetting the hammer.