WhatsApp uses the open Signal Protocol.
That's a bit misleading. WhatsApp uses Signal's end-to-end encryption scheme, but not Signal's networking protocol. It's still proprietary. Otherwise, we could have cross-messaging between Signal and Whatsapp.
Pedantic: I think you meant to say open whisper protocol, the end to end protocol which is Whatsapp copied from Signal.
That's a bit misleading. WhatsApp uses Signal's end-to-end encryption scheme, but not Signal's networking protocol. It's still proprietary. Otherwise, we could have cross-messaging between Signal and Whatsapp.