The notification only occurs when the Apple TV and Mac are running on the same WiFi network which hints that Apple is working on ways for Yosemite to interact with Apple TVs. Unfortunately, Continuity with Apple TV has not been outlined by Apple, and the latest developer previews of the software hint at no ways the feature will be used.
With Continuity, Apple could allow users to watch a movie on their device, and have it 'handoff' to the Apple TV, in conjunction with AirPlay. We would hope Apple's plans are a bit more ambitious, as the possibility of notifications for Phone Calls, SMS, and Messages would all be possible.
Many were disappointed yesterday when Apple dropped support for the 2010 720p Apple TV. Continuity requires Bluetooth LE 4.0, a feature that is only present in the latest Apple TVs, providing more evidence that Continuity is coming to the Apple TV.