The shortness of your driving test may have been partially due to your already having been licensed in another jurisdiction. I believe that some states test new drivers more extensively then they test experienced drivers.
International individuals are almost always required to take the full driving test simply because driving is so different in other countries and a lot of stuff doesn't apply to the US.
I too learned in the UK, and when I moved to the US I still took driving lessons for a few weeks before taking the test because driving on US roads is dramatically different from the UK and there is a lot of little nuances to get used to.