Quaternions are confusing, and more so once if you are trying to understand resulting angles by passing the Euler angles. The rotation vector 3 node needs the order of the inputs rearranges from that of the Quaternion from Euler angles A picture… thousand words:
I think it means that the axis has been flipped by a right angle along the (x axis?). Does the Quaternion.Rotation(Vector3) need to have its pin relabeled