Current iphones can be unlocked by asking siri for the time. I doubt the new iPhone security is much better.
Not sure if it's been fixed yet or not, but you can just turn off Siri from the lock screen.
1: http://lifehacker.com/ios-9-lock-screen-exploit-gives-evildo...
I have no idea how this works in regard to the encryption. It isn't likely anyone else here does either. They are just speculating.
I hope that it is good, but I don't trust it. No one should trust it.
I would look, but I don't own an iPhone.
I don't mean this as a claim that the iPhone is a secure device, since it obviously isn't in several different ways, but rather just that I can't reproduce this specific behavior.