I agree, quite odd. Perhaps they were planning on camping up above, as they certainly can't have been planning on taking the tram back down. According to the article, the sheriff's department was 'called to the tram station"--whatever that means--at 11.30 at night. Assuming an hour for lag time, it sounds like they called for help at around ten or eleven at night, from around 4000 feet. That would mean it took them around six hours to get to 4000 feet. Even I'm faster than that.

Their super slow time suggests they may have been carrying a very heavy load, i.e. camping equipment. If that's what happened ... climbing Skyline in the dark with a massive backpack is probably a pretty good way to take a fall, which it sounds like one of them did.
Q: How many therapists does it take to screw in a light bulb? A: Only one, but the light bulb has to want to change ...