The CWTime travel is a very familiar plot device in The Flash and the shows most recent episode was a reminder of that. Looking at what the series did with Reverse-Flash last year, it certainly isnt beyond them to concoct another villain from the future. The general thought is that Zoom is Jay Garrick from the future, either coming back to steer his younger self a certain way or because he knew this time in his life would allow him access to Barry Allen. The specifics of such an idea, from the time loops to the causality problems, are enough to make your head spin, but it certainly seems possible. It doesnt resolve how one Jay Garrick has seemingly been killed by Zoom, but it would go a long way to explaining how theres so many different versions of Teddy Sears running around. It also fits in with the comic book character, whose powers were based around controlling time as opposed to tapping into the speed force.