I'm calling bait and switch here. Aku is probably being sarcastic, because there's way the Samurai would really lose his sword. Scaramouche will probably keep on insisting which results in Aku checking revealing Jack does have it, but also seeing Jack and Ashi having a tender moment.

Cue Aku heading there to perform Unspeakable Evil.

either this or Aku believing it, and having a complete breakdown when he notices that Jack got it back and even got rid of his beard. poor Scaramouches going to be annihilated by him for that.