This might be a stretch, but I was thinking of the possibility maybe BG wasn't there in that area looking for females to attack. Maybe he was there because he was planning on robbing someone or one of the nearby houses, or scoping them out at the time. When he spotted the girls there by themselves, other ideas came to mind and he took advantage of the opportunity, so to speak. Probably not what happen, but just a thought that came to my mind.
jmo~
jmo~