Probably by trying to do it from first principles.

I'm sure a historian could give a more detailed explanation, but my guess is that:

Once steel meets flesh the Role Play ends and all that's left is Live Action, and to take a life is not a meager task when life as you knew it was a virtual mediation.

They brought a sword to a gun fight. Presumably they would have killed the landlord on the first go if he hadn't managed to shoot and kill on of the assailants first.

But it seems they went back later and finished the job. (He survived the original attack, only to be subsequently successfully murdered)

I've worked professionally on cases that have parallels.

It suffices to say people sometimes have second thoughts in the moment.

Most ‘samurai swords’ on the market are barely-functional wall-hangers. And the article describes it as a stabbing. Curved swords are actually quite hard to effectively stab with, so it’s hardly surprising that an untrained user using a poor-quality weapon incorrectly couldn’t cause a lethal wound.

Perhaps they weren't trying?

He knew his Judo well.