In the congress hearing zucky boy did, he was asked whether Facebook could read Messenger and WhatsApp messages
his response was to more or less trip over himself avowing that Facebook couldn't read WhatsApp messages—even when a follow up question specifically asked him about Messenger, he chose to ignore it and reaffirm that WhatsApp messages were private
i don't really see why he would've done that unless WhatsApp actually was encrypted, given that if he were lying about one it would be a lot easier to just lie about both