A little more than 2 years ago, Google purchased SageTV (both software and people) which is/was a very good package for watching live TV as well as providing full DVR services for over-the-air or non-encrypted cable stations. I suspect it is these same people who are doing much of the development work behind a Google settop box.
Google did buy moto which included their set top box division. mix that with the fact google is also a cable tv provider now. In the areas where they offer google fiber they offer gigabit inter net + tv. Is it possible that google is trying to expand their tv service out side their isp?