You are correct Dave, technically it is an upsell not an upgrade but what a deal. This is the second time we have received a call from Carnival a few days before our sail date.
The last time we were in an inside cabin and were offered an ocean view for $250. We did not take it because we did not feel it was worth it for a window.
This time we could not pass it up. Moving from an inside cabin to a balcony on the top deck for only $350 for the 3 of us was too good to pass on.