From The Verge: The inventor of iMessage leaves Apple for a messaging startup
I hate that term, “inventor”. I hate it because it’s not accurate. I’ve talked about this before in regards to the “father(s)” of the iPod—Tony Fadell, Jony Ive, Steve Jobs or Jon Rubinstein. Take your pick.
If we dig into the article a bit (ok, if we read the first 2 sentences) we get more details:

Andrew Vyrros, the man who led development on iMessage and FaceTime while at Apple, has left the company for messaging startup Layer. The company announced the news yesterday, but Vyrros left Apple several months ago, sources tell The Verge, where he was also responsible for Apple’s push notification services, iTunes Genius, Game Center, and Back To My Mac.
So he’s a lead developer, or likely a director of development. This helps.
Now if we had been reading about the designer “in charge of” the design of iMessage leaving Apple, we would have likely seen a very similar headline as this one.
Design is almost always a collaborative process, so awarding a single person as an inventor of a product is inaccurate.