Tell it to O’Reilly.
By the way, I can offer a point of reference from my personal experience. I once attended an airshow here in Colorado that ended up being attended by 300,000 people (far more than they expected - should have seen it coming since it involved the Thunderbirds and was free to attend). Anyway, while that was a massive crowd, I can definitely tell you that the crowd in D.C. was at least several times as large as the airshow crowd.
I also attended championship celebrations here for the Avalanche and Broncos that were estimated in the 150,000 - 450,000 range (depending on year) and again the crowd in D.C. was FAR larger than any of those.