Corona is not beer. It is made with corn. No beverage made with corn can be considered beer. Under the German Reinheitsgebot rules, for a beverage to be called beer, it should only be made with 4 ingredients: water, barley, hops, and yeast. That being said, I wouldn't mind seeing it offered on UA flights.

(p.s., be the same rules, Budweiser would not be considered beer, because it is brewed with rice.)