On my Baseball Scoring site, I have a post explaining in detail why even though Cespedes just sat there and looked at the ball, the correct official scoring of this play is a home run and no error. Feel free to check it out, if you want.
I still don't understand how some people think this guy is a gold-glove outfielder. He has a strong arm, but takes absolutely awful routes to balls, and occasionally makes bone-headed plays. Very glad he's not patrolling Fenway's outfield anymore.
For your entertainment purposes here are a bunch of other plays where batters got home runs, mainly due to fielder's misplays (but not errors!)
One week left of this 5 month hibernation!