Y'know, I believe it was an Asian stereotype in 19th Century America (around the time of the Gold Rush and the Transcontinental Railroad -- it rings a bell from a class I took in college), but to be perfectly honest I can't provide you with a concrete example.
I agree with you there Mrsbooks. As with the spanking scene that has been done to death on a thread, it is the authors imagination, also the behaviour of the time that the books are set in. Mr Willoughby was Chinese as far as I know and at the time they were considered this way.
...But Mr. Willoughby's first scene in Voyager does remind me a bit of Long Duk Dong's last scene in Sixteen Candles. http://www.npr.org/templates/story/st...
I agree that every 18th Century character's view of Willoughby is pretty historically accurate. I guess I'm just I'm not convinced the author's is.