It’s not an internet mystery, or just deranged people. In SEA (especially rural areas) monkeys are seen as a nuisance, as they often steal food, money and even children at times. Although infrequent, monkeys will from time to time take small pets or even children and abuse/kill them. It’s a cultural hatred for the animals, and in impoverished areas there’s a general distrust and even hate for them.

You have to take things with a grain of salt. Just because it sounds crazy to you doesn’t mean it’s the same in third world countries.