My sense is he wanted to walk to meet the coworker because he wanted to walk. In all it's simplicity, but for myriad possible reasons.
I'm dubious it's because of his directional skills, although I'd need to know more about his developmental issues. I think a born or at least bred? (same high school) local coworker could figure out how to pick him up directly if JJ so much as had his own address/intersection memorized. Esp if Fazoli's delivered, in which case I'd assume she had a working knowledge of the streets. All to which is a long way of saying...he could have wanted to stop somewhere, and then presumably keep going. So, where and why? And if to see someone, who?
If it was someone he really wanted (or needed) to physically see he'd go in person instead of calling, be it just to cancel plans, or otherwise. If it was someone he deemed an authority figure he was 'supposed' or 'encouraged' to see, he'd certainly stop by. In both cases, that's evidenced by the (apparently known) fact he was prepared (and seemed to want) to walk 4 miles, let alone the heat. So, I think it was for more than exercise. Sidebar, I think the nightly walks were taken in the same vein for a currently unknown purpose. Of course, maybe he was indeed just walking to smoke and then air out. As a kid, I myself went up on our roof and sat against the chimney because it was so blatantly hidden in plain sight. But if he was walking to smoke, I'm sure a co-worker could say whether he ever showed up smelling of cigarettes, and that might clear up a few things. So to speak.
Otherwise, if he had an actual destination, the waving flag for me is that he wanted to go Then (read: because he wouldn't be able to later). If just a new serious walking regime, he may have wanted to get it in time-wise. But...did he ever walk later in the day but before his usual shift? If not, that's not the reason he was walking. Meanwhile, there's an implied quasi-urgency for Then. No doubt he was conscientious, timely, respectful, a hard-worker, etc, etc. I think he also was quite sure he'd have the time for whatever stop he was making. So. Reasons to stop somewhere purposefully with an actual motive - dropping off/picking up/returning something, checking on/looking at something, hiding something, a non-phone or private communication (ie. brother not listening), ATM or pay a bill stop. If I wanted to get cloak and dagger, I'd also be interested in where the nearest USPS mailbox was. It looks like the type of area where one could be on a street corner. The clincher for all of this, is that based on what WE know, he intended to go to work and didn't think he'd be late to the school. And probably not in immediate danger.
Another scenario is he was walking, for whatever reason, and was called to a house/backyard on his route. "could you open this stuck jar lid for me, help me move the couch, connect this necklace clasp, or even an emergency, "come quick Timmy is (or isn't) in the well." Which would require justhteright timing and motive to come together and take him down. Unless he was also known to walk at that time (on a regular shift day) and this wasn't a one-time thing to be out at that time. If he occasionally put the bins away and then took a lap around the neighborhood, it's possible. Less fathomable is he took a shortcut through woods and passed a paranoid tweaker who reacted badly.
So I land back on he walked because he wanted to walk. Somewhere. To do something, or see someone. And if for a someone, that person either knows what happened, or wasn't aware something was going to happen but was there before or after. And as for a someone who knew him intimately, if a family member wasn't directly involved, but had an inkling of WHO was (including JJ himself), or WHY, it would take something significant in their mindsets/lives/beliefs to keep it under the radar but still want to find him. I think there was something brewing, and being called in early wasn't related, but either sped things up or altered a plan that was already set in motion.
I also don't think him wanting to walk excludes a car being involved. If he was picked up, it would have to be someone he knew. So it's certainly possible he left for the school while that person was en route to him and then picked him up. I don't think his cell records have been released. But I can see a scenario where he calls and says "I have to work, I'm heading out to a ride at the school now." Whether he planned to meet the driver right then or not, he's picked up for a quick meet on the way to the school, or he just gets in to enjoy the A/C, believing they're headed to the school. The ride didn't end at the school, and it's potentially related to whatever he did/whoever he saw on the nightly walks.
but I will say the skull is still being studied.
