New "Automatic App Sign-In" Feature?

I had the Zillow app on my 6s, but just downloaded it onto my 7 and opened it for the first time. iOS pop-up box came up with "Select Safari password," I chose my email, and BOOM! Logged me into my account. Awesome!

Is this new to iOS 10, or is it just an app-specific feature to Zillow? I've never seen this before. Either way, it's a very small but nifty feature and I hope to see more apps implement it.