This is a great idea and I'm hoping the topic hasn't yet moved on.
I've wondered this also and have come up with the theory that they had some sort of "run in" with him. Maybe he said something cranky,
- You shouldn't be up here , it's dangerous." (In a creepy way)
-Angry they were taking pictures even if at first not him.( Are you taking pictures of me?!)
-Did you girls throw something off this bridge? (this relates to sometimes kids/girls/boys) will be silly and toss things over a bridge or whatever.
My point is, I think he said something to purposely frighten them and when he turned around to come back, they were nervous even more. Taking on a position of adult authority, he said something like : "come with me I'm calling your parents or whatever" Taking them down the hill on a short cut.
Just my moo
and, by the way, I know I have misspelled