Once the agent has your password and takes the device into their back room for an hour, you have to assume that all data has been offloaded and the device has had an undetectable rootkit added.
This gentleman's expertise is in security and encryption and now he works for Apple, a company that makes products that the US government can't always crack. He was clearly targeted in his encounter because of his current position, based on the questions they were asking. Surreptitious access to his devices is highly desirable to US intelligence services.
Any device that you lose physical control of during these encounters must be presumed to be compromised and should be physically destroyed afterwards.
