My suspicion is that the AHJ is trying to make sure a full 20 amp load isn't plugged into a single outlet, i.e. 80% maximum loading allowed on a 20 amp outlet is 16 amps (unless all components are rated to operate at 100%).
That is not exactly what the NEC requires.
First lets think about a circuit with only one single 20 amp receptacle outlet connected to it.
That single 20 amp receptacle could be loaded 100%, the breaker feeding that receptacle could be loaded 100% for up to 3 hours or forever if it was 100% rated.
Now lets think of a circuit with two or more 20 amp receptacle outlets connected to it.
In this circuit we could plug in two or more items that total 20 amps and that 20 amps of load could again run 3 hours or forever with a 100% rated breaker.
The only time 80% comes into play is here.
210.21(B)(2) Total Cord-and-Plug-Connected Load. Where connected to a branch circuit supplying two or more receptacles or outlets, a receptacle shall not supply a total cord-and-plug-connected load in excess of the maximum specified in Table 210.21(B)(2).
So in a circuit with multiple outlets the total load can exceed 80% of the circuit rating but not at one particular receptacle.
