Let's be clear: This isn't the same as going to the Chrome Web Store in your Chrome browser and installing an extension. These are apps that will appear in the App Store and the Google Play store.
In addition, it still leaves a gap that Chrome users on Android have wanted filled for some time: There is no equivalent to the Chrome Web Store for Android's version of the browser, meaning users can't install useful extensions like Lastpass and the like.
Google made mobile Chrome apps available by providing developers with an early preview of a toolchain based on Apache Cordova, which is an open-source mobile development framework for building native mobile apps.
Things are still nascent, but as this matures, any Chrome desktop app that run on Windows, OS X and Chrome OS will be able to run on a mobile device.