We have here in Grand Rapids a kumbaya democratic mayor, whos first order of business as mayor was passing the resolution against the Patriot Act. So he probably gave the word. It was first announced as 8000, then 10, then 12 and when Kerry came on stage he announced it as 20,000.
Maybe the Mayor was wetting his whistle from a pocket flask and by the time Kerry got up to babble, the crowd did look like 20,000 to your Mayor.