A dirt yard is sufficient if it was to show off land. Grass is not required
It then took this association with rich and better and was used in the US to denote affluent and therefore segregated housing developments.
Generations ago those field would have been allowed to grow over because they could be cleared again on a whim.
These days you need six figured of engineering and permitting to clear acreage and ain't nobody gonna do that without a commercial use that can justify it.
Historically, using land with such properties for grass instead of crops was as sign of wealth, especially for large estates.