As mentioned in the article "Mob lynching isn’t a new phenomenon in India. According to some reports, there were more than 2,000 lynchings in India between 2000 and 2012 — well before WhatsApp was around."
I agree that WhatsApp has the potential to exacerbate such issues.
Because rumor mongering came about only with whatsapp, and gossiping with your neighbours is a phenomenon born straight from instant messaging.
People spread lies. Not platforms or machines. People. Via whatsapp, other IM services, email, printed leaflets, handwritten notes or voice. People do that.
I agree that WhatsApp has the potential to exacerbate such issues.