I agree with everyone else that it looks like a dangerous group ride. Seems like there are a lot of different abilities out there and less experienced are the cause of all the squirrellyness. It almost look as the guy that hit you was moving over because someone else might have been moving over on him.
People need to be predictable in groups like that or accidents will happen. The only thing predictable from what I saw was that it was mostly unpredictable. Passing on the right like that is a bad idea, if your hole closes... well you know what happens.