I too find this puzzling.
Sex is meant to be easy to determine from a pelvis.
I would treat this claim cautiously until we get some comments on it from other scientists. It's at least as possible that it's these two scientists, and not everyone else, who have goofed up. The correct designations are AL 288-1 and Sts 14. Lucy's skull was too incomplete to measure the brain. I've got a plan so cunning you could put a tail on it and call it a weasel.