Re: AHJ?
That's why the NFPA designated it the Authority Having Jurisdiction. It could be the guy with the most political clout. It could be the guy with the biggest muscles. It is always a political issue, and beyond the scope of the NEC. Let the AHJs slug it out, or ask your local lawyer. In my state, for matters of the building code the local AHJ is the town's BO, and the state AHJ is the State Building Inspector. The dog catcher is the AHJ, by the way, for all matters dealing with stray animals. And, in my house, my wife is the AHJ for all matters dealing with home decoration.
Your issue is straight forward. The engineer is not the AHJ. The BO is the AHJ. If they disagree, there are avenues of appeal.