They claim pretty directly otherwise, right on their faq page.
> WhatsApp end-to-end encryption ensures only you and the person you're communicating with can read what's sent, and nobody in between, not even WhatsApp.
Is your claim that Facebook is plainly lying about this? That would be a a pretty high-risk thing to do, even for them: their usual MO is to cover their abuses in a couple layers of legalese and deniability.
I dont think they do, or it would be of minimal value that WhatsApp is encrypted, considering the realistic threat model surrounding What's app use involves corporate and government snooping...