I flew China Southern CAN->LAX on the A380 and noticed 2nd level business prob had 10 seats available empty.

The announcement said there were in flight upgrades available to business class and I inquired and was told it was $1223 but you only got the seat eg no business class food.

I thought about it some more and think it's weird those guys didn't offer it at the gate but instead took it inflight.

Is this legit or was it a bribe / pocket money for the flight attendants?