My guess is that Boeing essentially gave the plane away in order to have one please, just one! success story at the Paris air show.

I can't imagine any airline making a deal at 50% list price with the current perception of that death trap with the public.

50% of list price, btw, is in the ballpark of usual discounts granted to end customers by Boeing and Airbus[1].

While I'm not privvy to any internals (obviously) my take is that IAG essentially gets the plane for free in exchange for a PR win for Boeing.

[1] https://en.wikipedia.org/wiki/Competition_between_Airbus_and...