The reasoning here is not the dissonance in behavior, but dissonance in belief.

A person can believe alcohol is not harmful to humans health without consuming alcohol, therefore it's morally acceptable if an alcohol producer does not consume alcohol.

But if they don't consume alcohol because they believe alcohol is harmful, while advertising (explicitly or implicitly by helping the alcohol company) that it is not harmful, then that is dishonesty. Because in this case, the person purposefully acts like they believe something for personal benefits, but actually they don't.