Google has changed the way that app indexing is handled on Google Search and is now showing any available related apps instead of just ones you already have installed.

App indexing in Google Search includes all apps now

Apps have been indexed in Google Search for quite some time already, but today Google has made some changes to the way it displays results. Previously, Google Search only showed the option to open results into apps that you already had installed on your device, but now they're are opening that up to apps you haven't installed. Adding support for app indexing requires developers to add some code to the app, then add deep links to their website, and then to tell Google they are there.

Says Google:

If you've implemented App Indexing, when indexed content from your app is relevant to a search done on Google on Android devices, people may start to see app install buttons for your app in search results. Tapping these buttons will take them to the Google Play store where they can install your app, then continue straight on to the right content within it.

Google will now show results from apps that users do not have installed on their devices, and give them an easy way to download the app. There are over 30 billion links into apps that Google's indexed. Even the Android Central app has been indexed for a few months now, so now you'll have no excuse to have not installed it.

Source: Google