FYI:

There are a few UA 2-cabin flights within the U.S. that are sold as three classes F, C, and Y.

Pax with F and C bookings are both accomodated in the same forward cabin.

Note: "C" is only bookable for passengers with a connecting international flight.

Because of this, AC's booking engine got confused and treated the flight as a "first class on a three class aircraft" award.