Thank you to the user from the local BMW internet forum – exactly he was the only one who did this experiment.
From one of the largest car part suppliers, he ordered the spark plug for B58, marked as OEM.
The spark plug was packed in the original BMW bow with proud lettering: ”BMW Group Original parts and accessories”. Price – more than acceptable – around 10 .. 11 EUR, instead of EUR 28 (dealers list price).

Here, how the side electrode of the spark plug looks like:

You can clearly see that nothing has been smoldered to it. But – maybe the circle is actually a cylinder of another metal pressed in the electrode?
The electrode was bent for the “expertise”:

And is scratched with a knife/pliers:

No, unfortunately, nothing is pressed inside the electrode! The side electrode is a “simple” one, not with a platinum “tip”. And this is the explanation of the price difference.
It is harder to explain why two different products are sold with the same code in the same type of boxes as from the same supplier! Why is one “original” BMW spare part “more original” than another?