I had not heard about this pilot being held for suspicion of smuggling weapons and ammunition. I doubt we'll never know the full extent of what is behind this story.

China releases FedEx pilot after nine month long detention
Chinese authorities have released a U.S. pilot for FedEx Corp (FDX.N) who was detained last year on suspicion of smuggling weapons and ammunition, the pilotís lawyer said.
Todd Hohn, a former U.S. Air Force pilot, was detained in September in the southern city of Guangzhou after he piloted a FedEx freighter aircraft. Chinese authorities said at the time they had found suspected air gun pellets in his luggage.
Hohnís detention occurred at a time when U.S. delivery giant FedEx had become one of the most high-profile corporate brands to get caught up in the U.S.-China trade dispute and other frictions.
The Memphis-based company had last year been the target of Chinese ire over shipping mistakes involving several packages, including parcels addressed to Chinaís Huawei Technologies Co [HWT.UL], which Washington has put on an export blacklist.