What kind of power does the new "Lucy" have? Are the powers demonstrated by Luffy's replacement as Lucy based on a Devil Fruit or Haki?

It might be haki because the way he blocked Jesus Burgess' attack, but he didn't say armament haki, instead used some kind of technique.
He was just using martial arts and haki, many characters fight using haki without saying it. You can tell he's using haki as his hands turn black.