If Boeing won it as suggested that virtually 'dumping' in trade terms and thats supposedly not allowed. AB won a very vigourous and tough competition to build the tankers and that meant they had to offer a very aggressive price and terms which Boeing could not match until the 'had' to. I am sure they will be compensated for that.
And I am not anti Boeing -when it comes to Military, and critical civil infrastructure , stuff you should always (be able) to buy your own. The UK of course being an exception to the Euro Bloc and the US model falls between two stalls and pays more for the wrong thing and has it made overseas as well