I'm pretty sure they're just regular models, at least one of them has a very large Instagram following. If you look to the twitter accounts of one of the flashers they actually do have a campaign for breast cancer awareness, where money donated is supposed to go towards paying medical bills of women in that situation, and they were planning to do this all along. Now I'm not sure if that's a particularly helpful for their campaign or if they just wanted to do it for the hell of it (why not both), but those are the perceived facts from their end.