When Portrait Mode was first released, they said that the camera array splits the field up into 9 (IIRC) depths based on distance. So probably what's happening here is they save the depth metadata so that you can adjust how blurred you want the background to be.
There's more to bokeh than 'how blurred is the background', it involves things like "how many leafs inside the lens are you using to control aperture".
You can "simplistically" (although still nicely) simulate this, of course.
