Olíamos a

Los vecinos hicieron una barbacoa y select ... oliéramosolíamosoleríamosolimos toda la comida deliciosa desde nuestro jardín. (The neighbours had a barbeque and we could smell all the delicious food from our garden.) I would like to ask why the preposition "a" is not used? According to the explanation in the lesson on the present tense it should be used when it concerns unintended smelling...