Everyone in he industry knows since decades that higher efficiency engines mean higher bypass ratio, which means larger fan diameter. So nobody can tell me that this came as a surprise for Boeing.
On those decisions the fish stinks always from the head. You see it in the automotive industry too, that it easier to drag the mid management levels to court on misconduct. While every one knows that expensive decisions (or decisions to save said expenses) will be made by top management. Especial if sums way above 6 figures are involved.
The game at court then played out is who knew what at what time. As if CEOs or top managers get paid for not knowing their trade.