I don't think that it's that unlikely that the same group that found the vehicle also noticed JH walking down the street. I'm assuming that when the groups were assigned to search they were doing a grid search and were assigned a particular area. They had been out looking all day and noticed their friend out walking, who doesn't stop to pick up a friend who is walking down the street?
I guess it doesn't seem that strange to me because even though I lived in a city of 130k I would inadvertently run into someone I knew almost every where I went. My husband was astonished. He had lived in the city for 6 years longer than I had when we got married, but I was always running into people we knew.
lol sorry for the quick O/T but my husband is like that too! He runs into people he knows or knew long ago everywhere including a vacation to Disneyland, several different times on trips to Tahoe, and even on a trip to Hawaii! Locally too, of course. I thought he was pulling my leg with the Hawaii one and he thought he was maybe losing his mind and mis-identified the person, until they waved and said "oh my gosh, (his name), Hi!! Can't believe we're in Hawaii at the same time."