General principle of silk screening could be find on Web sides like this:
http://www.silkscreenbiz.com/silkscreen3.htmSilk screening is easy, very technological and cheap method what provided very good results. This method often used to make PCB(printed curcus boards).
FED choose more expensive and less technological stamping process possibly because this pictures was made on already assembled cameras. Silk screening on assembled cameras will be hard and messy indeed. Possible to bust sale of this camera during Perestroika, FED decided to open cameras what was stock in warehouses and stamped them. I believe we had thread about FED-5 problems earlier?
If you look on this prints with magnified glass, or even without it

, you can see that quality of the pictures is not as good as on others commemorative cameras, while FED-5 made much later. Stamps only have black color and not as fine as let say 50-years of Soviet Power pictures. And on mine camera picture is not exactly horizontal

. So they most likely made by hands later, “after market” so to say.