>>532247680
They probably saw it as "Ken" + "zōru" sounds like a mangling of "sword" so let's make it a punny sword name in the spirit of the original. "Mack" comes from Mack the Knife, but claymore seems more like what it's supposed to be.
I feel like the Chinese name is probably closer to the intention though (the horned jack-'o-lanterm head?). Only thing is he's not an undead enemy, but that's before they're properly introduced in the sewers, so...