They also benefitted from some really strange decisions by Anaheim and Florida, who gave them solid young players and then gave them more players on top of that. They've gotten unbelievable goaltending from Fleury and a bunch of Dallas' minor league castoffs. And William Karlsson, who had never before scored more than 9 goals in a season, currently has 34 on 24% shooting (if Seguin shot 24%, he'd have 59 goals right now with 19 to play).
So basically: lots of incredible luck, some really shitty GMing from other teams, and a team full of Eakin/Haula/Smith types who are super fast and aggressive and push the puck up ice.
Oh, and there's always the Vegas Flu, which affects players in their mid-20s who travel to Vegas the night before. Dallas overcame it by flying in with the players' dads. Anaheim just flew in on game day and thumped the Knights. But playing every single home game against a hungover team that got no sleep the previous night is a big reason why they're 24-8 at home.