We have these things called binoculars, telescopes, cameras and drones. All of which are able to observe subjects from a safe distance.

Binoculars, telescopes and cameras will tell you little about what islanders are doing inside the forest where they hunt if you are using them from the ocean. Drones flying over Sentinel Island would violate Indian law and whoever did it would be in huge trouble. Their data would likely be disregarded due to the ethical issues.

On top of that, if they heard a drone coming, they might just change what they normally do.

Like these people. Hunting becomes less of an issue suddenly when there's a flying threat.

https://www.telegraph.co.uk/news/worldnews/southamerica/brazil/2049750/Uncontacted-Amazonian-tribe-photographed.html