I don't think I remember that stuff. What was it exactly?
In the industrial world it is called thermal spraying, also metallizing. It's done with everything from steel, to copper, aluminum, chromium, you name it onto all types of substrate.
Back, I dont know when, maybe 1990s could be, you'd see ads in magazines and such for 'metal spraying' being done by franchise guys kind of like the dustless blasting now.
Anyways, as the name sounds, it attaches and builds up a sealed prepared surface with metal instead of a filler, goal to be avoiding panel replacement and since it's actual metal nothing to bubble up or all out.
They really used to push it back when repop panels weren't everywhere for everything and what was there sucked for fit.
I did a Google search and this weird site seems to list different systems: https://www.tmsmetalizing.com/industries/automotive-rust-repair-metal-filling-corrosion-control.html
But the application seemed to be perforated panels that were too expensive or hard to find to change, things not repoped, etc.