Okay - Alternative explanation, is it possible he was in the area to partake in a separate crime, maybe handling stolen goods, drugs or something similar - He then sighted Libby, maybe spoken to her and she then walks away as she might be a bit weirded out by this man, he then finishes what ever he was there to do and then returns home. He didn't come forward for fear of being caught.
This would also support an interview given to the press by a relative of the person the press have named -
I also have to agree with another post that says he wasn't seemingly putting too much effort into whatever he was placing in the car, so it's unlikely it could have been a person, but it does look very strange and I doubt the police would have released actual footage of an abduction if that's what they believed it was - I think this man would have been charged by now if that footage was as compelling as it "appears" to be.