There are unfortunately situations where the only way to reach someone is via WhatsApp. I have avoided them but i can see WhatsApp in a VM being useful for those purposes.
i believe they are referring to the whatsapp bug that the saudi prince used on jeff bezos. simply sending bezos a message gave the saudi prince root access on his phone and he dumped all his messages and photos and released them to the press. running in a vm would just have whatsapp so they can send and receive messages without exposing all the private information on their phone in case of some 0day