Can we get a bit more backstory on what this mod is, or the arrangement between the two of you?
From the info supplied I can see that Furdle is seriously overreacting and is on one of his massive ego-trips, but if you have been unfair to him or haven't held up a deal properly, then I can't be surprised at him getting angry.
I'm certain that what ever the issue is though it doesn't warrant petty threats. Furdle's just a childish yobbo.