If it's true that they implemented end-to-end encryption (as it seems), it's unlikely that they do.
Nothing is unlikely when they haven't even admitted in public that they have adopted it. At the moment end-to-end encryption on Whatsapp is nothing but vaporware.
Could they call it end-to-end if the ends are the devices and the server (never cleartext, but they have the key)? Or, in combination with what is available through FB, is the metadata telling enough?