A counseling statement can be given for just about any reason. There is nothing that says it has to be reasonable. However common sense dictates that it should be reasonable and it must be factual. Based on the information you provided, you placed yourself in a position in which it was reasonable for leadership to assume you were drinking an alcoholic beverage. The leadership apparently chose not to confront you at the bar potentially to avoid an Article 15 situation, if you were drinking beer.
By making an observation of the incident and documenting it in a counseling statement they were firing a shot across the bow. They are giving you a warning, that should you place yourself in that position again they will most likely confront you on the issue and proceed with more stringent enforcement.