The decoy passcode feature should boot into a separate partition that looks like a normal phone setup, and during that time quietly erase the user's actual data. They would never have known if it worked like this.
Probably, but it will be more valuable for society for him to be tried and found not guilty, setting a legal precedent.
And the court gets to assume that whatever was on that phone hurts your case, regardless of whether or not it did.
It would've been better if he'd crossed the border with a phone already factory reset and just restore it after entry.