I agree it could be oxidation. But to sure, were the hop varieties you mentioned the ones used throughout the whole process ? Because if the last round of dry hopping were done with some of the newer varieties like Mosaic, Citra, El Dorado, Calypso, etc., there is definitely a fruity 'sweet' perception imparted by those hops. And I don't know how long ago the beer was brewed, but hop bitterness fades over time and can make a beer come across as more malty sweet. Not buying the alcohol reduction argument here.