What does poor use of automatic gears mean on a DMV road test?

I'll guess what it might mean, but you should have asked the examiner. I'm guessing you didn't stop the car between shifting between drive and reverse. If it was anything else, you need to think back and remember how you were driving. Failing to signal is sloppy and lazy, illegal and dangerous to other traffic.

There should be no "use of automatic gears" required by you on a road test, other than shifting from park to drive or reverse, etc.

You put in drive and leave in drive to go forward. You put in R to reverse.  You have a problem moving the lever from one to the other? You got REAL problems. Pay for schooling.

As its an auto and selects the gears as required Id have who ever took you for the test ask the tester what does poor use of the gears actually mean?

I think you have been stiched on that point

I'm guessing bad habits like not coming to a complete stop before changing modes. It's odd how whoever was teaching you didn't reprimand you for similar mistakes earlier. 

It likely means you were shifting past Reverse to park or not getting to R and stopping at Neutral thinking you were in Reverse or going into Drive or shifting past Drive to a lower gear when going forward. I suspect it was on the 3pt and parallel testing where there is a lot of gear changes.