He was an adventurer. He would go to remote and weird places all the time, usually without any kind of primordial tribespeople to convert. Odds are he was just on another adventure, rather than him feeling that these people really needed jesus.
https://www.cnn.com/2018/11/21/asia/andaman-nicobar-us-missi...
Did Chau learn any Sentinelese? How was he planning on doing the proselytizing?
Also, not to nitpick, but the article does have other errors. For example, it says "Just more than a dozen people" live on the island, whereas all sources I can find say between 50 and 400 people live there.