In German, a person from Berlin and a jelly doughnut are both called a "Berliner", therefore he made no mistake (it sounds like "Berlina", because the German "r" isn't as "strong" as the English/American).
"Berliner" is simply an adjective and means "someone/something from Berlin".

Greetings from Cologne, where the (dialect) adjective for the city's name is also the name for the local type of beer.