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Part of it is engine dynamics. Hold a steady speed for a bit with steady air intake and fuel delivery, you get steady emissions (and numbers) from the tail pipe.
Real driving has very little steadiness to it and the car's reaction to pressing your foot on the gas, or going up/down a grade or just engine load from power steering & A/C changes.
In short, when you stomp on the gas, you get more unburned fuel out the tail pipe. Thus the higher HC number. Which in your case was too hight.
But, was that because he accelerated too quickly, meaning falling outside the parameters of the test? That I couldn't tell you because I don't know the test procedure in AZ.
Here in NY, the down-state (think NYC and surrounding heavily populated areas) emissions test has the tester work through a sequence of set speeds and has specific window of time to reach each one. The computer monitors the speed on a dyno while the tail pipe sniffer monitors the emissions. In the end a set of numbers appears for the max and min (and also a pass & fail). If the test falls outside of the necessary speed envelop during the test, the computer invalidates the test and has the mechanic start again.
HTH -CTH
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