Not sure why you are confused. The credit report apparently showed you owing ~$30,000 and American Express is telling you that this was too high relative to your income. The fact that you were able to pay off all the accounts this time is evidently not as important to them as the fact that you spent more than their formula says you can afford.
Why are you selling the car?
Bought a nice benz about 2 years ago based on an old income. That incomes been reduced so the payments on the car have become a larger impact then it used to be. That plus looking at the devaluation of the car and what i still owe on it, its better to just cut it. That aside, why would amex base the decision off what i owe them, when based on the date they ran the credit check, it was AFTER i submitted all my payments, but BEFORE they finished posting. Seems like willful ignorance on their part to cite my high use of their cards when they know full well that they are currently processing my full payment for the entire balance.