He is 100% correct in that assertion (if you take lethal weapon to mean gun, in this case I think that's a safe assumption although he should have been more specific), you need to have a reason to own a gun in Australia and self-defence is not a recognised reason. It's the same in the UK, if you have a valid reason to own a gun and you must use it in self defence then you're protected by the use of reasonable force (or whatever it was recently reworded to), you can't own a gun for self-defence though. We do have an odd Personal Protection Weapon licence system in the UK which applies in very specific circumstances (usually in NI with ex-security types) so we aren't as cut and dry as Australia in that regard.