Umm, you need both arms to get extra attacks (for Angel of Blood's death company dreadnought), and he lost the heavy flamer arm. It's on page 60 of the codex.
The weapon destroyed result was on the Heavy Flamer it seems, you don't actually lose the arm. To lose the extra attack you'd need to have had the CCW destroyed.Interestingly, the wording says nothing specific about if one arm is destroyed. Though I guess "has two blood talons" is fairly straightforward. Looks like a re-roll is in order then.
Check on Page 84 of the BRB.