I would disagree with Q on Berlin--anyone who is a fan of films, theatre, or music before the rock era knows Berlin. And they teach him in school now. And the under 30's with those tastes are children of the information age, and have access to way more, They've seen the Fred Astaire movies, and White Christmas, Holiday Inn, Easter Parade, etc, either on AMC, TMC, or Netflix. They can find the soundtracks to all the movies on Spotify, and, in ten seconds, can come up with things like "Irving Berlin: A Tribute to his Music, which is a collection of original recordings from 1921-1931. He's way more accessible than he was, even 40 years ago.

As to the OP, I think it's a sly joke that is a tribute to his facility with ragtime(they used to kid about things like that once), which, incidentally, was in it's third decade of popularity when ARB was first a hit. Ben Harney, who was regarded as the father of Ragtime because he brought it from Louisville to Vaudville, was accused of "passing", though his father and mother were both from distinguished Southern families, so it was not exactly a new thought.