While it's not possible to say with certainty, this segment of the movie may have been completely invented. It shows a group of Million Moms March protestors, apparently protesting Heston's appearance in Flint on October 17, 2000. One of them says precisely what Moore wants to hear -- that they wonder why Heston is coming here, how could NRA come here, I'm "shocked and appalled," it's as if the rub their faces in the tragedy.
I can't claim certainty, but there are several anomalous things about the footage of the protest.
1. Although the protestor is given prominent treatment, her name is not given. Moore is generally good about showing or speaking a person's name. He shows, for instance, the name of the speaker at the Columbine/Denver protest, and the names of individual bank clerks in the bank scene.
2. When Moore shows stock footage from newscast teams, he follows the usual requirement of attributing it to its source. He does this in the Flint segment, when he shows Heston's answering a reporter's questions after the rally. He doesn't attribute his own footage, of course.
No attribution is given for the interview of the protestor, suggesting that Moore filmed it himself. But as I note on the main page most of Moore's filming appears to be around summer 2001. I've seen no indication he'd begun filming by October 2000.
3. The protestor says just what Moore would want someone to say, although they are rather strange statements when we understand what was really going on in Flint, as opposed to the impression Moore wants to create.
It's an election rally for Bush, height of the campaign season in a key state with voting only a few weeks away, Gore and Bush both giving speeches and holding rallies in the Flint area. Why would a protestor wonder why Heston is coming here? Why would they have come to protest the rally without knowing its obvious purpose? Why would they guess at an answer, and then say he must be doing it to rub their faces in the tragedy, when that was eight months before? The interview sounds all to much like something created in 2001, perhaps when Moore felt he needed an additional touch here to create the impression he desired.
4. Heston's rally at Flint was from 6 to 7:30 PM. Sunset on October 17, 2000 was at 6:50. Yet the filming is in broad daylight, and does not seem to be toward sundown.
5. The protestor interviewed is wearing a T shirt without jacket or sweater. Behind them can be seen someone in short sleeves. But on October 17, 2000, Flint had a. low of 43, a high of 63. At 5:53 PM it was 59 (same source).
6. While the filming is so arranged as to allow little view of the background, you can see leafy trees, and they're not pines. This is late October in Michigan?
While I'm not certain, I am quite suspicious that this is not a real interview of a protestor, but that Moore simply lined up a few actors or friends in Million Moms t-shirts, posed them in a parking lot, and told them what he wanted said.