Why everyone is so convinced Facebook is spying on their conversations

Bipul Lama believes Facebook is spying on him. 
And he's got proof, sort of. Lama performed a test. For two days, all he talked about was Kit-Kats. 
"The next day, all I saw on my Instagram and Facebook were Kit-Kat ads," Lama said. 
After his Kit-Kat experiment, he successfully repeated it with chatter about Lysol. The 23-year-old musician is now more convinced than ever that Facebook is listening to his conversations through his phone's microphone. 
"It listens to key words