It is a standard practice among tree companies that the “tree” and the “stump” are two different things. In other words, “tree removal” does not automatically include grinding the stump. The “stump” is what is left in the ground after the tree is cut and removed. Stump removal involves a process of grinding it up with a special machine. The end result are relatively fine wood shavings usually mixed with some of the surround soil). A “stump” becomes a “root ball” if and when the tree uproots pulling the stump and connected roots out of the ground. Removing a “root ball” involves the same grinding process as a stump, except it is usually a bit messier and the wood material may not be as fine since it is loose when ground.
You should also know that “surface roots” are considered separate from any stump grinding process. These are roots extending from the stump that are visible. Some trees have notoriously large and numerous surface roots. These could potentially be ground as well but are additional to the stump itself.