At the moment, the Edge browser is updated as part of Microsoft's Windows Update system. However, in a session held last week at the Microsoft Ignite 2016 conference, (via Thurrott.com), the company revealed that in the future, the browser will be updated in the Windows Store, just like any Windows 10 UWP app. This should allow for more features to be added to the browser on a more rapid schedule. The reason why the engine behind the browser will continue to be updated via Windows Update is because it is also used in other UWP apps and will need more internal testing before updates are released to the public.
There's no word on when this new Edge update system will be enabled, but it's possible that it will go live as part of Microsoft's "Redstone 2" feature upgrade to Windows 10, which is reportedly due sometime in early 2017.