I do think someone doesn't know german that well...

they can drop the "ein" before and it wont sound weird.

ala the "Ich bin ein berliner" bit from JFK... he said, I am a berliner, a popular donut in berlin.. if he had said "Ich bin Berliner" the spectors would have understood that as "I am a Berliner, not a jelly donut"

thats why there was laughter and such, popular joke in german class