Google is always testing one or two little things in search results, but this is a more significant change. We're starting to see the option to install apps from inside Google search results without opening the Play Store. Not everyone is getting this yet, but enough are that it's probably in the early stages of a wide rollout.
You can test this yourself by opening the Google app and searching for the name of an app. It will appear at the top of the results with an install button—this part is true for everyone. However, most people are booted into the Play Store when they tap it. Those with the new feature will see a permission popup just like they would in the Play Store, then a miniature Play Store frame appears so it can be installed. It's really neat.
This might only work from the Google app, not Chrome (that's common with similar features). Some users report that this started happening a month ago or more, but only recently has it started appearing widely enough that we got tipped about it. Take a look at your search results and you might find it's already live for you.
- Tregan Emmett