That is one sad story; originally there were a couple of other guys with him, and they’d tangle with local villagers when they’d set fires at night. Afterwards, when asked why they did that, he explained that they were signaling Japan that they were ready for the re-taking of the Philippines. They had a radio and heard news of the war in Vietnam - and assumed we were fighting the same Viet-Minh that had plagued Japan’s occupation there; when they heard news of the Olympics in Japan, they interpreted that as a sign the war was going well.
Some of these guys couldn’t adjust to life in modern Japan, and set up a little colony in Brazil.