Based on inland rules, I can see a couple possibilities regarding court
decision and appeal.
Since we are talking whistle signals, since the outbound vessel proposed
a stbd to stbd passage and the crossing vessel agreed to this, but then
was unable to make the turn and collided. The court could hold this
vessel to have the main fault since they should have known whether or
not they could make the required turn and if there was doubt, should
have blown the danger signal and not have agreed to the stbd/stbd passage.
However, since you are discussing ships, it can be assumed that there
were pilots aboard both vessels. This being the case and since nowadays,
pilots are being held to a higher degree of responsibility, on appeal, a
court might decide that the outbound pilot was equally responsible,
since his higher training and experience should have indicated that this
may not have been the best passing agreement.
Without all the info that was available to the courts, it's tough to
guess their thinking process, but the above are possibles.

otn