It sounds like the cyclist that got injured is equally at fault for riding too close to his "friend". If this happened in the US, the guy that hit the tree branch would sue his friend for riding too close and colliding with him!
Drafting is a nice way to save energy, but it can be dangerous on a bike like it is in a car. Riding 2x2 in a bike lane seems like a bad idea because it doesn't leave enough room for the cyclists, nor does it leave enough room for cars to get by safely.
There are not a lot of details about the accident in the article, but my point is to ride sensibly and you shouldn't need insurance. It's hard to do a lot of damage to anything but yourself on a bike.