Gravel is a mixture of sand and small stones, aka dirt, as it would be removed from the ground. Every dirt road in this state is a gravel road.
Sift out the sand and you have stone that can be sorted for pea stone or crushed stone; all of which are refined aggregate. Gravel is unrefined aggregate, minus the removal of rocks and larger stones. You can add refined aggregate to an existing "dirt" driveway and it will eventually mix with the existing material, it is no longer refined and has become gravel.
Unless you are saying their driveway was in scratched off condition, which is the first process in developing a raw building lot (removing the organic matter at the surface of the forest floor). That would most definitely be a significant upgrade.
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