I thought that was just based on URLs. Similarly when I open a yelp.com link in my mobile browser it asks me whether to open it using the Yelp app or the browser.
That's yelp.com detecting your mobile browser and asking whether to redirect you to a URL using its private (yelp:// or somesuch) URL schema, which the app is then registered as the handler for.
This, on the other hand, is Google sending you directly to a yelp://-or-somesuch URL.
Basically, Google is taking charge of doing the client-negotiation step, so (if this catches on) sites don't have to worry about doing that redirect themselves any more.
On (newer versions of) iOS, you don't need to send someone to, say, yelp://rest_of_url to link them to the app anymore. In iOS 9 we have Universal App Links[0] that let you perform a redirect from an actual website link into your app.
For example, if you have Twitter for iOS installed on iOS 9 and you click on a link to https://twitter.com in a Google search result, you switch into the app's main screen immediately.
