As far as I'm aware of, Facebook collects and stores all the meta-data WhatsApp generates. Which means, that it can provide a list of phone numbers, IP addresse

As far as I'm aware of, Facebook collects and stores all the meta-data WhatsApp generates. Which means, that it can provide a list of phone numbers, IP addresses, or even GPS coordinates(?) of the people who contacted the journalist at any specific time. So, even if the messages are encrypted, a person can still be tracked down.