Q.Why Did My Ginger Root Sprout?
I used a store bought ginger root to grow indoors and it sprouted. It died a few months later and after about 5 months, with no water, it sprouted again on its own in bone dry dirt. How is this possible with no water?

Certified GKH Gardening Expert
It, likely, reached the sweet spot at just barely moist as it was drying. This would trigger it to sprout and continue to do so. It was sprouted before the soil dried, fully.
Wetting too much after sprouting, or leaving it in saturated soil for too long can kill it off.
I must say- It is quite fortunate that it sprouted! Most markets will have them sprayed with something that keeps them from sprouting.
Here is an article to help you with growing Ginger:
https://www.gardeningknowhow.com/edible/herbs/ginger/growing-ginger.htm