Pretty much. A compketely blank phone is a clear sign that it's wiped, and why would you do that, unless you have sonething to hide, hmm? A phone with a couple of weeks of boring use, maybe a few photos of nice sunsets, a few messages, a take-out ordering app, some boring history in the web browser, and maybe a login to a social media account that follows some celebs and an old school friends or two who don't seem to post any more, just says you got a new phone a while back and you're fairly boring.
Obviously, if they actually have something on you, or they want to pin something on you, those precautions won't actually help much.
I don't think the difference between him physically triggering the wipe and him giving them the code that triggered the wipe would have much effect from a legal point of view. In both cases he deliberately took an action he knew would lead to the destruction of the data. I think his defense's approach of challenging the legality of the stop is probably much safer.
I suspect that the prosecution would like to set precedent that you can't claim to be under duress when a lawful authority is performing a search, so the defence staying away from that area is probably a good idea.