yeah, that definitely was not the sequence of events signal started in about 2014-15 and their protocol was used by the rest of them, so-called "double ratchet" protocol, and you may also have heard of "OTR" messaging, that also came around the same time, it was out of the same school of cryptography development signal was born out of the merger of the FIRST SMS based auth service, and everything else uses that now, whatsapp, telegram, viber, they all use that, but it was invented by Redphone here's some history

Open Whisper Systems - Wikipedia