Both girls were family members, but maybe they only wanted to target one but couldn't manage that.
I agree that it might have been a random abduction, but a couple of things make me lean against it. One, the very narrow timeline, and two, the fact that a local would be more likely to know that area well.
If the girls were taken from the BignTall parking lot, then I would lean towards random abduction.
But if it was a random perp passing through, I don't think he would try going to that little lake and dumping the bikes. imo
But if the bikes were dumped there, OR if the girls were taken from there, it makes me think a local was responsible. And the very narrow timeline makes me think it was a specific kidnapping by a family acquaintance,