IMO he was trying to get back to his car in the fastest possible time. If he knew the girls had been dropped off at the park (and I think he did) then he had to logically know that someone was going to arrive to pick the girls up. That person or persons is/are going to search the park first... going to go right straight to the bridge first, imo. There is a walking path along the ridge of the woods below the cemetery but it takes a person straight to the bridge and a choice of taking the drop off path or the main path out of the park and someone looking for the girls isn't going to just walk by saying, "Hello" this time. He's going to be questioned: "Have you seen 2 girls?" He can't take the chance of being stopped and questioned! He can't cross the river and try to cross over that railway bridge because he, of all people knows that's a trap. If he starts crossing the bridge, someone might be coming across the bridge from the other direction. Even if he manages to cross there, he still needs to walk the 3/4 mile of trail to the trailhead and could run into people that way. He can head south at the end of the bridge but, looking at the overhead of the park, you'll see that he now has made his trip to his car almost impossible to do in any kind of timely manner... it's the worst choice of all if LE is called quickly. He can't afford to be seen inside that park all muddied up and bloody. He has no way of knowing if whoever might come to pick the girls up won't call 911 immediately. He walks along the road trying to disassociate himself from the park... he is a guy who might not be noticed or paid any attention to at all by any drivers... for those who might see him, they probably won't stop and question him... they might assume he fell off a dirt bike... or got into a fist fight... or got kicked off by a horse... or had an accident with some farming equipment and is walking to a farm along that road. He took his chances in other words. The woman who claimed to see him didn't stop... didn't question him... remember that most people who would see him have no idea 2 girls are missing and murdered. He probably had his head down and looked to the right or faked walking away from the road due to an oncoming vehicle... remember the young girl witness on the trail who said she "was trying to see his face" yet she couldn't. She was mere feet from him. He's wearing a hoodie and cars might drive by quickly. Yes, he just took his chances... had to get to his car before LE was called. He probably turned his head away from any cameras that probably wouldn't have been able to give a good visual ID anyway.
And, there is always the possibility he went that way because HIS ride was late but he hadn't given up on the idea that his ride would come along. If that was so, his ride would not find him if he was in the park. For all we know, someone picked him up before he had to walk too far anyway. I'm sure, if there is an accomplice, they would be able to communicate by phone when it was time to be picked up.
This is all just my speculation and opinion.
edit to clarify
