Clear? Easy to understand? Maybe to someone who knows about the activation lock feature. To someone who doesn't know, that message is cryptic and hard to understand.
"Sign in with the Apple ID that was used to set up this iPhone."
"But what? I haven't setup this iPhone yet! What Apple ID?"
And there is no guarantee that the current owner can recognize that the truncated email address that shows up belongs to the previous owner. Many people have multiple emails, so the email that is used for Apple ID is not necessarily the same as the one used for corresponding with other people.
There's already been cases of people posting in the iOS 7 subforum asking for help with getting past the activation lock. Believe me, once iOS 7 goes into general release, there will be a flood of threads asking for help.