I read that it originally just said "bone" instead of rib. And it's speculated that they meant the penis bone that is present in many mammals except for humans.
Kinda makes sense. It's a reproductive organ after all.
The rib story is a rewrite from an older Sumerian myth, Enki and Ninhursag, which did point to a rib specifically. We know that because that was a pun in Sumerian - the rib (ti) is used to give birth to the goddess Ninti (lady of life, here changed to lady rib, then also lady of the month). She's one of seven goddesses created / born out of a body part where Enki is in pain (throat, eye, arm, etc.)