He's crushing a voice of dissent in his mining operation.
Eh, as Icon says downthread, killing everyone in the crew is highly counterproductive (there's a fear-rebellion threshold that he's definitely crossing if this is his default reaction to dissent), and there's no reason not to believe this woman about the gas leak. If he's trying to do anything here beyond tormenting this lady, he's doin' it wrong, and is an idiot more than anything else. If he's totally indifferent to the actual mining work being done, though, and merely relishes the misery (whether because he's genuinely collecting slaves just to have a pool of sufferers handy, or because he's got a long-enough term goal and enough resources that a tunnel collapse is not a meaningful setback), the scene makes more sense and he's a more formidable villain.
Hey, maybe it's Blue Snowman in a REALLY good male-impersonator disguise!