I actually am a native, American English speaker, and while I am aware that the common usage refers to somebody who is able to handle loss without taking offense, I did not rest on the assumption that the common usage was the relevant usage here. I would consider the meaning of the quote given the common usage inaccurate, as I find the implication that a gracious loser is necessarily an unmotivated loser incorrect. Therefore, I left open the possibility that the quote might use a less common meaning of the term "good loser".