That makes sense to me.
I do wonder why Brian all of a sudden asked the hitchhikers to stop the van though so he could get out.
I think I can answer this in a MOO fashion.
According to Miranda Baker's account which included maps, it appears that MB and her boyfriend were taking the
scenic route to Grand Teton. Once they turned off 191 and headed toward Jackson Dam, BL immediately realized this and knew he needed to get out of the car. MOO.
BL needed to get back to Spread Creek - not Grand Teton. And, for this, he needed them to continue on 191. As a side note, MB and BF could have gotten to their destination by staying on 191, and I believe this is probably what BL expected, but they chose not to. Realizing this, he panicked, got out and told them he was going across the street to the parking lot to hitch another ride. It appears he did just this.
As for why he refused to allow the second hitch hiking witness to take him into the campground and to his van, MOO is that GP was already gone. For nearly 2 days is what I think but not fact (I have felt she was gone on the 27th, after Merry Piglets and that the 29th was an alibi, a shower, discarding evidence, or maybe all of the above MOO). He couldn't have this witness see him return to an empty van and/or risk her parking the car and stepping out. IMOO, BL was
always thinking ahead. He was calculated in his moves.
If you look at the attached map, you'll see that once you reach Jackson Lake Dam, you are already on your way to the scenic road. This road would be traveled at a much slower speed and would have placed him very far away from Spread Creek. IMOO, he couldn't have this because he was planning that evening to get out of there and on the road back to Florida. This is and has always been MOO. This is not fact.
Edited to include correct map
Google Maps