Someone else has already done the research and has identified what this object is.
It's part of a baby buggy wheel. It's not just a hubcap. It's an assembly. It's a heavy rim that fits into the wheel hub, an integral bearing sleeve and a hubcap, all together. The hubcap is on our left and the bearing sleeve is on our right.
Let's sort some things out.
This is a hubcap on an "artillery wheel" type auto wheel.
It's properly a hub grease cap. It fits directly over the outside end of the bearing to keep the grease clean.
This is a wheel cover.
The actual hubcap is under the wheel cover.
The hubcap on a car is threaded and screws into or onto the wheel hub - or (I think) is secured with some kind of pin. No matter. It doesn't just snap on and off. The hub grease cap has a true function. To seal the bearing and protect it from contamination.
Auto wheel covers (so-called hubcaps) snap on. They're mostly decorative.
Baby buggy - (pram, perambulator, baby carriage, baby coach)
Old fashioned baby buggy wheels seem to usually (or exclusively) use sleeve bearings.
Sleeve bearing
Baby buggy wheel. The "back" side.
Green arrow - bearing journal
Red arrow - bearing sleeve
Same wheel flipped 180 degrees. The hubcap is visible.
Blue arrow - wheel hub
Purple arrow - hubcap - More properly, the hub grease cap.
The spokes are attached to the wheel hub - a hollow tube. The sleeve bearing is inside the wheel hub.
There are simple snap on baby buggy hubcaps.
This baby buggy "hubcap" is for sale on eBay.
https://www.ebay.ca/itm/191489296486
This seems to be a particular type of "push on" hubcap with a heavy piece of metal that pushes into the wheel hub. That heavy rim has an integral bearing sleeve. The whole thing is one assembly.
Purple arrow - hubcap
Blue arrow - rim that fits into the wheel hub
Red arrow - integral bearing sleeve
My guess is that - in this particular type of wheel - this whole assembly pushes into the wheel hub. The wheel hub has another bearing sleeve. So there are two separate bearing sleeves on the bearing journal.
I'll try to find what this type of wheel looks like, but that won't be easy.
Our Flying Saucer is this type of baby buggy assembly - heavy rim, integral bearing sleeve and cap. It has a lot more heft then a separate "hubcap." Which would make it easier to throw higher and with more stability. You'd put some spin on it, not to get some kind of other-worldly photo effect, but to give it spin stabilization.
Considering that this is the natural way this part would fit on the baby buggy this isn't sideways. In any case you'd put in your hand in this position because you'd be able get spin on it, and it would get less air drag.
It's all together a more natural way to throw the thing. If you throw it underhanded, you could put the proper spin (spinning on its minor axis) by letting it roll out of your hand. If it were sitting flat in your palm, the way it would naturally sit on a table... how do you get it to spin on its minor axis? Hold it by the rim with your fingertips and spin it and throw it at the same time somehow? It doesn't work.
No reason to speculate that Kibel wanted it "sideways" for any other reason. It's just what works best.
Yellow arrow - An integral, decorative, part of the hubcap.
Red arrow - bearing sleeve
You can see a specular reflection of blue sky/white cloud on the top one fifth part of bearing sleeve, and a darker specular reflection of something below the object on the lower four fifths of the bearing sleeve.
People have been assuming that the yellow arrow is pointing to the nut on a service bell. Service bells don't have an integral nut. The nut is always a separate piece. The bell sits on an internal clapper assembly. The nut is a separate piece and screws onto the internal assembly.
A note about the surface of the hubcap. This is not polished or "brushed" metal. This is plated. Probably chrome plated. If it's really old it might be nickel plated. It has a mirror-like surface.
And about the spin giving it an other-worldly photo effect. It wouldn't. This is a mirror-like surface. A spinning mirror would not appear blurred. What we see are the specular reflections of the environment around the object. The specular reflections on the surface don't "spin."
Any other-worldly hazy appearance comes from poor resolution and lateral motion blur. Not from a flying saucer's inter-dimensional drive, or from a worldly spin.