The trail isn't shown on the park map because for some reason they don't list the "quiet walkways" on the trail maps. The trail that you were on is maintained by the park until it crosses Thunderhead prong as a quiet walkway. If you look at my attached pic the area in grey shows this. There are not any shelters up this trail, but a handful of off-trail routes do exist such as Thunderhead manway, Defeat Ridge manway, Sam's creek manway going up to Starkey Gap or Sugar Cove, and The trail from the Caddy on Lynn Camp over Green Cove Gap down to Sam's. I would guess they were camping illegally or maybe did green cove gap, or just fished on way out camping somewhere else legally.
And Climbing up to Starkey Gap isn't nearly as hard as climbing up Bee Cove which was over 1000 feet in the last 1/4 mile
Brown line is old rail grade. One on bottom L goes up Defeat ridge. One bottom right goes up Sam's