Two points about this one.
(1) Ewwwww. Creepy!! Reading the notes the defendant sent to the 15-year old just made my skin crawl.
(2) This is a classic example of an overly agressive view of what counts as "harmless error". There's no way the result in this case is crystal clear, and I could easily see a jury deciding there was reasonable doubt. My sense is that -- perhaps partly due to (1) -- the Court of Appeal nonetheless themselves concluded, albeit on a cold reocrd, that the defendant was guilty. Hence the result.
Do I think the guy's guilty? Sure. Probably. Was there a real defense in this one? Totally. And could the error in letting the jury know about the defendant's (totally understandable) refusal to talk to the police have affected the verdict? Sure it could. (Which, I have no doubt, is why the prosecutor highlighted it during closing arguments.)
We use harmless error way too much, I think. Including here.
P.S. - That said, to reiterate: Ewwwwww!