I imagine that the first step (Make a map) is still done as a group. I also imagine that this step probably still involves some brainstorming-like interaction as you’re trying to decide on the problem. For everyone to then go off on their own to create their own competing solutions on day 2, it’s essential that everyone agrees on the problem they are trying to solve.

It seems to me the main distinction here is that “brainstorming” is still part of this process, but it’s being focused on the problem only, and not the solution.