Err. I think he's just stressing physical security is the first line of defense and proposing a solution in a case where it is compromised. (Sure, if they can physically hold you, then they can hack into the server via your camera and delete uploaded pictures, but that's a harder task than breaking a locally secret based encryption)

You can MiTM a phone without people ever knowing. If police steal a camera they may as well take the key holder too.

It could just be stolen, but both cases would be helped by uploading and deleting.