I'd want to know if height plays a role.
From a brief scouring of google, the tall variant is more common in taller women. It's also more common in African women over Eurasians (which would explain the more typical body shape there), and is associated with larger buttocks (again, expected). I'm going to speculate here and say that the tall pelvis is associated not with
height, but with
long legs.
It is a more "android" or male type of pelvis, and I've noticed that men very often have more projecting buttocks than women, although this is sometimes disguised by womens' greater fat deposition in that area. In fact I'd say it's probably the rule if you only counted muscle and not fat.
A comment on reddit states that it is associated with "assimilation of the sacral body to the last vertabrae":
Smaller mothers of reddit: have you had any complications giving birth? : AskWomen
This is new info for me, but makes sense, as when I'm stressed my back feels tight and not straight. I've also posted before about both aspirin and K2 causing cracking or "crunchiness" of joints in the back and hip, as have other members (I've noticed it in my arm and femur joints too). There's something major going on here with bone fusion.
If the pelvis really did temporarily fuse to the last vertebrae, it would also mean a greater lordotic effect when trying to rest your hips in a neutral pose. I experience this, and here's a diagram I made illustrating why this would happen:
https://i.imgur.com/fDgz9RB.png
Note how the pelvis has the same tilt (it should be naturally slightly tilted forward), but if fusion occurs, it has to tilt against the second-to-last vertabrae, which makes it stick out more. This also make the natural waistline higher up, as the indent in the back ascends, and this is very evocative of today's popularity of "high-waisted" jeans, contrasted to the 2000's era of "low cut" and "hip hugging" jeans.