It was not improper for the police officer to have arrested you with respect to a driving under the influence of alcohol or a controlled substance based upon the fact pattern that you have written about. The reason was that there was circumstantial evidence that you had committed the crime that you have written about.You had alcohol on your person, were in a vehicle with keys in the ignition. The issue is whether the prosecution will be able to prove the crime beyond a reasonable doubt. I suggest that you consult with a criminal defense attorney about the matter you are writing about.