I rather suspect that neither the people who posed the question, nor the people who answered it had the vaguest idea of the processes that had been used to make the pistols.
I’m sure you are right about that, but I still think it can be done. Metallic elements would not be removed during the forging, they are in the steel/iron alloy and would only be lost at the same rate as the steel they are in, so comparing element ratios to detect ET contamination would work for cobalt, iridium, gallium, germanium. And these days, scientists who want to confirm the origin of a material that is probably ET rely on isotope levels and/or ratios. Two of the six cosmogenic radionuclides used for confirmation of off-earth origin are metals, 26aluminum and 10beryllium – if they were at elevated levels in the meteoric iron I believe some of that would carry over through the forge welding – I know an awful lot about forge welding, but only a little cosmochemistry, so I’m at the opposite end of the spectrum from the scientists running the ISIS machine... To really do it right, you would have to make a boatload of meteorite/terrestrial steel samples and take an awful lot of measurements to establish a baseline, and that is the real limiting factor, no grant money to do that part of the investigation!