A ball joint that isn't?

Has anyone seen a balljoint like this before? It's the top one from a 2000 P38, the bottom one was a normal ball in socket. The car had very asymetric handling, now it's fine with a new (ball in socket) joint. Once the hub carrier was off, the bottom one was the usual floppy worn out and this one wouldn't move at all, even with big hammer persuasion. Not surprising once you see it cut open. What's the point in something like this? It could have a little give in the nylon but no real movement, it's just going to lock the suspension?
The second pic is the lower (normal) ball joint that came off.
Just curious if anyone knows.

It is a normal upper ball joint.
The lower ball joint is a more traditional unit that fits into a collar that can adjust the height of the hub assembly to suit the oil seal. This allows any differences in the manufacturing process
One tip while doing the bottom ball joint is.... "DON'T MOVE THE BLOODY COLLAR"!

it allows rotation

Thankfully I didn't move the collar on the bottom joint. I had a go at it... then wondered what it was and looked it up
Thanks for the info, never thought there might be different types. Is this just to allow small movements?

How long do you keep old newspapers ???

That's one of my new ones, hasn't even gone yellow yet. Keep the old stock for special jobs