What’s Up With the Ending?

The book wraps up with a touching moment of Artemis reuniting with his mother and thinking about how he'll have to be more secretive with his illegal schemes now (so sentimental, that one) and you think that's it. So why smack the reader in the face with an off-the-wall epilogue? 

Suddenly everything gets a little eerie when we realize we've been reading a case file written by a psychologist—but is he the narrator? The epilogue sounds totally different from the prologue, so where is this leaving us? If Dr. Argon was telling us the whole story, wouldn't that mean our impressions of Artemis were formed based on the opinion of his enemies? The only really concrete thing the ending gives us is knowledge that there is more to come.