Agree it's a fine line, but once you have a confirmed seat on the flight, it really becomes more in your favor in situations like this.

What if after everyone boarded, including yourself, the plane ends up having a mechanical and everyone ends up with a five hour wait for repair? Are you not entitled to a food/beverage airport voucher and/or other compensation just because you were originally a standby? I think once you have boarding pass in hand, you are part of that flight.

Thus, the GA had to pull you from your flight and regular DBC or other agreeable terms should apply.