I think they did not run because they were young and didn't have complete confidence in their instinct that he was coming after them. To me he is looking purposely nonchalant in the video, looking down, hands in pocket, trying to be unassuming. All they knew is that they were trapped and isolated with a man approaching and it was scary enough that Libby wanted him on record. Ugh, I can feel the terror just typing it. But they grappled with whether he was truly after them and he played them by not paying attention until he was close enough to be in control. I almost wish Libby had not filmed him because sometimes looking through a screen can take you out of the moment a bit. I so wish they had just followed their gut and taken off screaming down that hill while they were ahead of him - but honestly, for young girls, that would be a very bold move to basically accuse an adult of bad intentions loudly and publicly before he had said or done anything. I feel they just froze and hoped for the best.