Perhaps it's just me, but I don't get it. I thought an atheist was someone who believes there is no god. Prayer is communicating with God. Why would an atheist want to go to such a thing? I haven't spoken to these folks, so I don't know what they're thinking, but it kind of sounds like they're being rabble-rousers. Perhaps that's too strong a word, maybe it's more like instigators...I don't know, but it's odd. I mean, this came to the attention of the media. What are they trying to do? Stir up trouble?
My humble advice is this: life is too short, much shorter than you realize. Don't waste it looking for trouble. If you want to go to a prayer meeting, just show up. I doubt the people holding it, will have a problem with that. And if they do, they need to be in prayer, so see...it works out for everyone.