Where was he speaking?
Did it cost anything to attend his speech? How much?
Was it advertised in media that catered to African Americans?
I have often known of famous African Americans having a speaking engagement in our area, but often, it is not exactly in town, or there is often a heavy charge to see the person (especially if you are talking about carrying your kids), and many of these engagements are known of (happened across) a day or two before the event (giving little or no time to prepare to attend, time wise or financially) or known of after the event has already taken place because it was advertised in a magazine, newspaper/newsletter, on a radio show or via some subscription or membership required news medium.