I'm glad you found that, because there MUST be a complete circuit for current to flow (assuming an imbalance, as someone else noted).
The fact that the earth isn't obviously a "wire" is lost on some people who simply assume earth is ground potential and that's that.
But, that's OK.
That's because *both* ways of thinking work just fine, simply because the earth contains more electrons than anything on earth (which goes without saying). It's like the car frame example. Exactly. Only on a huge scale.
So, both concepts work simply because earth and the car frame are special things that don't look like wires, but, they act both like zero potential and like wires.
Specifically, the earth is both a zero potential, and a huge conductor back to the power company.
As Gallileo supposedly said on his deathbed to those who couldn't fathom the wonders of the earth ... "and yet, it does".