I understand what it said. My question was, why did it show a cross buy option with an airport when I went to buy GSX but did not show this when I chose the airport?
I believe to have answered this question: one thing is what triggers a discount, and another thing is what gets discounted. GSX was in the list of the things that triggers a discount, but not in the list of things that can be discounted. In fact, according to the description of the promotion (which only mentions airports being discounted by other airports) GSX shouldn't have been in either list.
But, since we already had XPOI behaving as an airport, there's really no reason why GSX should't be there too, so we added GSX to the list of things that can be discounted, not only to the list of things that can trigger a discount as it was before.