I've often wondered if........let's say, they willingly went with this guy at first. Not sure if they were the type or not but, to be honest, I was 13/14 when me and my friends had our first beer. And, being pretty stupid, there were many times me and my friends would go hang out with guys who cat called us from houses, parks, etc. Especially if they said they had beer. Once we had it, we thought it was "cool" to always try and get it. Was that stupid? ABSOLUTELY!! But you know how you sort of feel invincible at that age. Especially if you're with a friend(s). Well, that was us. Maybe it was them too. And of course if you had asked our parents back then if we drank or would ever go with strangers, our parents would have said, NO WAY! But that was not true, in reality.
I wonder if this guy maybe came off to them as friendly enough and encouraged them to go see/do "whatever". They may have been a little leery but went anyway but just in case, decided to record the situation anyway.
For EXAMPLE, let's say the guy approaches them. Says something like, hey girls, I have some beer. Want one? Maybe some other convo happens in-between. Libby feels a little skeptical and maybe reaches into her pocket to start recording on her phone. So they ask, where at/where is it? And he says, down the hill. They follow and who knows what happens next.
Anyway, just a thought/theory/etc. Because, to me he seems calm and cool when he's saying, down the hill. Almost like he's just telling them he has something down there for them (i.e., beer) or there is something to be seen (i.e., an animal, better pic opportunity, etc) down there that may interest them. Who knows. Just trying to think back to myself at their age and I did a heck of a lot of really questionable things that I never even gave a second thought until I was an adult.