This is one feature many users will welcome, but for others it's something they'll want to keep off. Automatic software updates are convenient in that you don't have to keep tabs on when new software is available and remember to install it. But this can pose a problem when new software doesn't work as it should, which recently happened with Apple and the Apple TV. After the most recent update many users were complaining of a bricked device, so the update was pulled until Apple could resolve the issues.
With that in mind, you'll want to make sure you have the automatic update setting set to your preference. On your Apple TV launch the Settings app, then visit General > Software Updates.
Here you'll find the option to check for an update, along with the option to enable (or disable) automatic updates. I checked my Apple TVs after updating them and had one default to automatic updates being on, with the other two set to off by default. I'm not sure what caused the lone unit to set itself to on, but it's a good reminder to always check these settings.