اِعْشَوْشَبَتِ الْأَرْضُ
Translation: The ground became thickly covered with grass.
The source uses this example for intensification. The point is conspicuous abundance of grass, not simply the presence of some grass.
FeatureObservation
Basic situationGrass grows on the land
Intensified meaningGrass becomes plentiful
SyntaxThe land itself undergoes the condition
An intensified meaning does not automatically convert an intransitive verb into a transitive one.