I heard him on Radio 5 about 9.30 this morning - I don't know about his credentials in terms of the far right, buy I can tell you that his stuff relating to Weapons Intelligence was utter bollocks.
It's probably that he was asked about something outside of his specialism and instead of say 'sorry, I don't know' he tried to bluff it out.
He tried to pin the weapon - what looks like an AR-15 type hunting rifle, modified illegally - on the NZDF by saying that that's the most likely source of the expertise required to modify the weapon (he even suggest that it was an NZDF weapon that had been stolen by NZDF personnel acting for the murderer), buying fact it's the exact opposite - the NZDF would have no need to have that knowledge because they have armouries full of automatic and semi-automatic weapons, and probably don't actually have any single shot weapons.
It is, of course, possible that this is an NZDF rifle (they are moving from the Steyr rifle used by the Irish Army to an AR-15 derivative, so they are around in NZ) but the blokes reasoning is batshit.
If it's a civilian, but converted weapon, it's much more likely it was done with online help from US or AU's gun nuts. 5 minutes on Google will show you how to do it and where to get the bits.