He didn't smash the phone to pieces, he gave LE a hammer and they smashed the phone to pieces. It's entirely LE's own fault this happened -- they shouldn't have been trying to get into that phone, and it's their own fault it went wrong.

Though I would expect courts to consider that he knew LE planned to enter the provided PIN, and that the duress PIN would then result in the phone being wiped, and therefore accuse him of doing the wiping anyway.

But I don't think it's this guy's fault at all. LE is the one who asked him under duress, he easily could've feared for his life, and he did no direct harm. It was self-defense at worst.