Some context:
Iowa City is Berkeley on the Plains. It is liberal's liberal college town, a town where protesting is a near profession and moonbattery is the center of the political spectrum. There are many precincts there that vote 80%+ Democrat, and even a sizeable Green Party contingent.
More importantly though, it is very close in travel time to Cedar Rapids and the Quad Cities, two of the larger population centers in Iowa, and you can bet many came down from those towns to see her
And then you have, due to it's location and being the intersection of two interstates, also being within an hour's drive to a majority of the eastern half of Iowa, where most of the population is, and also most of the Democrats. Many would have traveled from those places too.
If she stiffed over 1000 people, that is a monumental campaign blunder here. Communities are tight, word will spread.