Which of the following is a white wine not classified as a house wine?

The correct answer is Cupcake - Chardonnay because it indicates a specific brand of Chardonnay that is not classified as a house wine at Outback Steakhouse. House wines are typically used to refer to the restaurant's standard selections offered at a lower price point, and they often include popular varietals that the establishment serves consistently. Since the other options either are classified as house wines or do not represent a white wine, Cupcake - Chardonnay stands out as a distinct choice.

In the context of the options provided, Pinot Grigio reference clearly identifies a house wine, while both Red Diamond - Chardonnay and Cabernet are associated with house selections. Thus, Cupcake represents a product that is recognized for its brand and quality, distinguishing it from the routine offerings at the restaurant.