Interestingly enough, the informant heard this same urban legend from two different sources. He heard it from his dad first, but then heard it again from a counselor when he was at summer camp.
There are tunnels that run beneath UCLA, and supposedly someone has been living there for decades. One time, a group of UCLA students decided to go exploring in the tunnels. They became hopelessly lost and stumbled upon his living area, complete with a mattress and dishes, etc. The students freaked out and ran through the pitch-black tunnels where they got separated from each other. One of them turned around and saw the tunnel hermit. He tried to grab her, but she got away and a week later they boarded up the tunnels.
He’s not sure if it’s true or not. He doesn’t think students got lost down in the tunnels, but maybe that there could have been someone living down there at some point. He says the legend is fairly popular with his friends at UCLA, though some of them tell the legend a little differently. In one variation of the informant’s version, the girl who found the hermit is actually caught and killed or, in another, caught and held hostage in the tunnels and remains down there still. These variations typical of oral folklore probably arose from misunderstandings, or perhaps from each subsequent storyteller’s attempt to make the tale scarier for whoever was listening.