I dunno - I don't think challenging someone counts as self-defense. "In anger" suggests passion, especially if it involves jealousy, and I always interpreted "down went his hand for the gun that he wore" as meaning the stranger reached for his gun but didn't get to it in time. Which he clearly didn't, seeing as how he ended up dead. "My challenge was answered" doesn't paint the other guy as being the aggressor. I suppose it's all in how you look at it...

So in anger I challenged his right for the love of this maiden
Down went his hand for the gun that he wore
My challenge was answered in less than a heart-beat
The handsome young stranger lay dead on the floor