I think a reasonable meaning (that the author might accept given the quoted statement) might go like “I live in a neighborhood with a bunch of other successful business owners or highly paid professionals, I must be pretty middle class”. As you rightly point out, that makes you pretty dang successful — more than “middle” seems to imply.

Of course, historically, that is the middle class. But no one cares about history.

From what I can tell, anyone richer than me is clearly not middle class; those bastards are rich. I’m clearly middle class, and hardworking, too. And damn it would suck to be poor in the US.