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."
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.”
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I hate to say that Physics.org is wrong, but if you quoted them completely then they are. Magnetism is not created by moving iron except in a magnetic field. We are within the suns magnetic field. When the earth spins the iron spins with it and is also is moving through the suns magnetic field. Similar to the way a transformer works another field is created around the spinning earth. It is somewhat more complicated than that because not only is the earth spinning, the molten iron is also moving inside the earth independently of the rotation, but there is another force to contend with and that is the orbiting earth moving through the Sun’s magnetic field. All those motions produce magnetic fields. Without the Sun’s fields though there would be little if any field produced by earth’s movement. The molten iron has very little permeability, that is in the absence of an external magnetic field the magnetism in the iron would quickly die away.
The flow of iron circulating in the earth is very, very slow, but the rotation of the earth at the equator is about 1000 miles per hour and the earth’s movement through the orbit is much faster than that. You can see how then that these huge forces can generate such large magnetic fields.
There are many other considerations but most are pretty minor.