You're talking about a carbon steel wrench that rusted away on the bottom of a stainless steel tank due to Galvanic corrosion. It is an extremely common problem for submerged metals. It is usually mitigated by sacrificial zinc anodes, which are slowly dissolved byb the water, protecting submerged structural and mechanical conponents of boats, ships, pipelines, and structures.
The claim from that article is bogus. It was written by someone who does not understand what they are talking about, for an audience that doesn't care.