You are correct; they look for low creatine levels to see if you're urine is diluted indicating you have been drinking tons of water to flush out any drugs in your system. Why high creatine levels would bother them? My only guess would be that they suspect you took one of those products from GNC which help you pass a drug
test. Creatine is one of the things included in these drug
test pass kits, so that you can drink tons of water and still not fail the
test for diluted urine. I'm guessing they think you used one of these and took too much, hence the high creatine levels. Drink more water before you go in next time to dilute the creatine in your urine somewhat.
~Joffa