Horace is speaking there of the Vergil of the transpadane period: the reference is to the Eclogues.
And he stands in this perhaps not so much for himself as for a transpadane school.
Two constitutions were needed for new-born states, the republics known thus far as the transpadane and the Cispadane.
The disquiet of the outlying cities on the borders of Lombardy was due to a desire for union with the transpadane Republic.
Vergil himself—if, as seems likely, the Catalepton be a genuine work of Vergil—did not escape the transpadane fashion.