I recognize the Sun Tropics Laverne tag. It's odd to me some Feijoa are pruned like that from the nursery and sold as Feijoa tree, and then the normal bushy growth will be sold as Feijoa bush.
It's true if you top it will bush out which I think is preferred normal growth. Either way you should be getting some tasty fruit next fall/winter. This is one of the most care free , automatic fruiting , drought tolerant fruits we can grow in Nor. Cal.