It is not a he said-she said sort of thing. It is a "person who allowed a search which resulted in incriminating evidence" said - "cop that saw the evidence" said thing. Accused people tell stories that differ from the police all the time, juries still convict.
Quit living in a fantasy land, reasonable doubt does not favor a person that consented to a search which resulted in incriminating evidence and is now trying to hide it. The jury is going to think: "He is hiding something, he is guilty." The jury is not going to think: "OOOOOO an encrypted hard drive! Technicality! Ignore everything the officer said!"
It is not feasible that there is something else on the hard drive. If there was it would have been brought up already, the fact nothing but this 5th amendment argument was raised means there is nothing else. And if there was something else it is now waived and irrelevant. That argument is gone.
The only way the accused can rebut what the officer was is to get on the stand and testify. That is not going to happen because the only time an accused person should take the stand is when they have an air tight story which is sympathetic to the jury. Otherwise the prosecution will tear him a new one.
While it is true you don't have to open your trunk when stopped for a speeding ticket, that argument is irrelevant for two reasons.
1. This is a border crossing, not a traffic stop. Different rules apply, like it or not.
2. If you want to continue with the car analogy, a more analogous fact pattern is: The accused was stopped, he opened his trunk which has a combination lock voluntarily, the cops say the weed, the accused shut the trunk and refuses to give the combination. The incriminating evidence has already been discovered, the time to refuse to open the trunk already passed. He can't refuse to reopen the trunk now. This isn't a 5th amendment right, it is discovery.
This guy consented to a search, the search resulted in incriminating evidence that he is now trying to hide. No "what about" or "what if" hypotheticals are going to change the fact the accused already gave the prosecution all the evidence to convict him.