That may be the case, but if you have ever trained a classifier you know that expecting a model to generalize when given data that it's never seen before is not

That may be the case, but if you have ever trained a classifier you know that expecting a model to generalize when given data that it's never seen before is not something you should usually expect. It doesn't mean that there is no discernible difference between the two classes, just that the model has overfit to the narrow subset of data and things that were previously immutable (e.g. the color of the wine) were not actually immutable.