I think a more reasonable explanation is that the author of the article uses WhatsApp more than he realizes. It's possible that WhatsApp is maliciously polling

I think a more reasonable explanation is that the author of the article uses WhatsApp more than he realizes. It's possible that WhatsApp is maliciously polling your contact list all the time, but it's more probable that some views access your contact list and the article's author ended up on that screen very often.