Hey Sarah! Nice to hear from you

The author did an AMA on reddit and from what I have read, he just went to talk to the neighbours to ask what it was like to be there around that time and since the show came out. He didn't ask him if he saw anything, WS (the neighbour) just told him the info, and the author spoke to the daughter too (the one we hear about in the police calls), who said that WS has been saying this all along, but no one asked him (it reminds me of the eyewitness in the Ryan Fergusson case... no one once asked her if it was Ryan that she saw that night).
As for the direction..... according to the article, WS said INTO the quarry, but it doesn't sound like he watched or knows if they went into the quarry or if they turned and went into the back of Avery's Salvage. It sure would be interesting to know if that area was searched for maybe uhmmm a wheel well that seems to be missing from the RAV4! In the AMA, the author was asked about the "speeding" at 40mph and how it didn't seem that fast.... he said if the road was anything like it was when he was there, it was not a smooth road and going 40mph would be "speeding", if that makes sense.
Also, for what it's worth.... the family has commented too that he has been telling them this for years, it's not "new" to them.
As for seeing the police vehicles.... well, he said that he heard on the news that the key was found the next day and we know that most of the evidence was found after the key was found too, so it's definitely interesting. And we know he's not lying about that because we have the police calls to back it up, which I think gives some credibility to his story about the RAV4/Jeep sighting IMO