Sounds like possible espionage. Chinese spies spook easily and flee the country long before the FBI gets its shit together.
Believe everyone can put together the type of events that cause sudden behavior changes like that. (Hint: money offers or family threats)
I don't know what motivated this guy's disappearance but you don't get quietly fired, scrubbed from public association and have the FBI raid your apartment when you're a victim of abduction. We know some sort of federal crime took place to justify the raid so my guess is the guy is not an abductee but a fugitive.
I am not saying that definitely happened, but it's a narrative which more or less fits the facts.