There are plenty of metal stamping companies that can produce shielding cans. Just google for EMI shielding cans…
There are even metallized plastic shields. This design allows for visual inspection of a board after reflow and then press-fitting the plastic shield onto the board so that shielding can be added without an additional reflow step.
This has been around for a very long time. I remember dissecting dead electronics as kid in the ‘60s and lots of them had shielded sections. Most TVs had them. I recall FM IF sections were often shielded. This was to prevent self interference to/from other parts of the circuit. There is nothing special about the metal cages - cheap bent sheet metal. Though solderability is important in many applications. The only requirements are a good ground connection and that it not have holes.
Note also that having a metal (or metalized plastic) case for the circuit board fulfills a lot of the shielding requirements for external EMI.