They may not be entirely out to sea. Years ago ('80s) the head of IT decided that all the documentation we produced should be subjected to proper version control (not the code, just the documentation). To that end, we had to provide him with the source files for our documentation (on 5.25" floppies), which were then secured in a filing cabinet. Overall, not a bad concept, if the implementation was a bit primitive. Six months later, we needed to update the documentation for a project, so we asked for the relevant files. No response for a week, so we asked again. Eventually, we learned that the cabinet was open at the bottom and had been sitting directly over the incoming mains to the plant; all disks were blank. We had to hire typists to re-create the files from hard copies of the documents.
Now, that was the mains for a manufacturing plant, so the field was probably stronger than at home, but it is possible that the magnetic field of the mains could have a measurable effect. More likely that these folks are bat crap crazy.