The company explanation is wrong, really except for the first sentence.
The correct hand waving explanation would be much longer.
Materials are composed of atoms which contain electrons, and electrons have intrinsic magnetic moments and specific orbitals around atoms that are not affected by temperature. The molecular bonds are affected at high temperatures.
Ordinarily, the enormous number of electrons in a material are arranged such that their magnetic moments (both orbital and intrinsic) cancel out. This is due, to some extent, to electrons combining into pairs with opposite intrinsic magnetic moments as a result of the Pauli exclusion principle (see electron configuration), or combining into filled subshells with zero net orbital motion. In both cases, the electron arrangement is so as to exactly cancel the magnetic moments from each electron. Moreover, even when the electron configuration is such that there are unpaired electrons and/or non-filled subshells, it is often the case that the various electrons in the solid will contribute magnetic moments that point in different, random directions, so that the material will not be magnetic.
However, sometimes—either spontaneously, or owing to an applied external magnetic field—each of the electron magnetic moments will be, on average, lined up. Then the material can produce a net total magnetic field, which can potentially be quite strong.
For magnetic materials, in the formation of the solid state of the atoms, there are small magnetic domains where the energetics are advantageous to building up a large magnetic moment from the collective moment of the electrons. These domains can be disturbed or even destroyed by heating, because heat affects the vibrational and rotational energies of the atoms and molecules in a lattice, and supply energy that will again randomize the directions of the magnetic moments.
For specific atoms, iron is the first discovered since ancient times, the term magnet comes from Magnesia a region in Greece where it was first discovered as magnesian stones. The creation of the "stones" from the cooling magma, gave them a collective magnetic moment and they became permanent magnets. Other solids can be manipulated with external magnetic fields so that their domain orientation generates a permanent magnetic field.
So heat can at first destroy the domain orientation which builds up the field,and then even the domains themselves if the material melts even partially.
