It might have been wrong. Has Lucy's bipedel posture been discredited?
Let us just say uncertain(whatever that means).
When Lucy [ = Australopithecus afarensis] was the only known hominid species of her time, she was the best [ = so far only] candidate to carry the human ancestral lineage. Now she has a contemporary, so there's another candidate. That would seem to be the uncertainty, not that she's suddenly a chimp as is often claimed in the kind of pamphlet trash which only a naysaying Luddite dolt would credit.
Bipedal. (Sheesh!)