Ask HN: What does the iphone actually encrypt?

Today I ran across of a recent video ( https://www.youtube.com/watch?v=Jk7GaO_vAW8 ) which shows someone using siri to bypass the passcode and be able to access all photos and contacts. Shouldnt this be impossible according to apple? I thought the only way to unlock this data was with the correct PIN. What other data might also be unencrypted?