Because Will Cathcart is the lead of WhatsApp, not Facebook. As is mentioned clearly in the title. It's not like they are hiding the association as his quote is immediately followed up by:

> WhatsApp’s owner, Facebook, has reasons to pounce on Apple for privacy concerns.

To be fair. Apple is opening up the door to allow Facebook to pounce.

Likely relevant as WhatsApp does not always see eye-to-eye with mother FB, notably on privacy issues. Source: used to work there.