See, my only issue with it is that this shows Smyth as evil, but also an idiot, and idiots don't impress me.
Ignoring a problem like a methane explosion doesn't make it go away, and what does it benefit Smyth that there's a mammoth explosion in his mine? It wastes slaves and destroys the mining work already achieved. A truly malevolent bastard would have thanked the woman, taken precautions against an explosion, and THEN dealt with her for insubordiantion.
And killing THAT many productive slaves also seemed... excessive. I dunno, megalomaniacal villains these days, always trying TOO hard.