I think the author was thinking of things we can sell in China that would take up cargo space on a plane so that freight planes carrying cargo from China didn't

I think the author was thinking of things we can sell in China that would take up cargo space on a plane so that freight planes carrying cargo from China didn't make the trip back empty - they'd have American goods to sell in China. Yes, the US can sell a lot of things, but are these physical items created here to take up cargo space? Sure, Microsoft makes a lot of video games and software, but we're probably not literally shipping Xboxes or video games from the US to China. Yes, the US might be selling that, but it probably isn't using cargo space for return flights.