So how could it arc out at two seperate electrodes unless each provided exactly the same value to ground?

It doesn't.

Even if they did work as advertised your still distributing the same amount of spark energy across a larger area, resulting in a larger but weaker flame kernel.

After they got in trouble with the FTC, the second arc was removed from their advertising. They may show it flickering between the two in some ads, but the print ads had one arc removed.

Michael