A lot of people don't realize that the fuselage of this plane isn't even made by Boeing, it's made by Spirit AeroSystems which also makes components for Airbus. We don't really know who to blame here until the investigation concludes.
True, but the main Spirit Aerosystems factories making Airbus components are in the UK, except for "central section panels" of the A350, which are made in the USA.
The British factories used to be BAE and Bombardier factories, so it's very possible for there to be different working methods, culture etc.