Given that a cartridge case and primer are all brass (I believe even the anvils in most primers are non-ferrous), would that even be possible?
In this case it doesn't matter, that's not what happened
As stated in the article, it is believed that the magnetic field pulled the firing pin safety block out of the way, making the pistol NOT drop safe. This implies that the firing pin did in fact strike the primer, although the article does not specifically state that it did.
The article clearly stated that the empty cartridge case was found inside the chamber of the pistol, the slide did not move back due to the thumb safety being on.