I’m not sure the flood had anything to do with it but, the earths magnetic field is largely generated from the earth passing through the magnetic field of the sun. When there are changes in the sun then some of those changes could easily affect the earth’s magnetic field. When there is a CME that is targeted at the earth I could see where it would be possible to have a short term effect but how a long term effect could be produced in a small area is certainly confusing.
I haven't heard that explanation before.
According to Physics.org: "Our planet's magnetic field is believed to be generated deep down in the Earth's core. ... The Coriolis force, resulting from the Earth's spin, also causes swirling whirlpools. This flow of liquid iron generates electric currents, which in turn produce magnetic fields."