Well, to be honest, I don’t fully understand this ceremony either. My previous encounter with it and prior knowledge of it has been related to architecture and new buildings. When the roof was put on a new building, mochi was thrown down from the roof. At some point, mochi was replaced with a variety of candy and snack foods.
A similar type of ceremony is apparently also related to Shintoism and sometimes held at shrines, though I’ve never seen one held at a shrine. I have no idea what the meaning of the red carpets is, but I assume that it is connected to Shintoism. I’ll see what I can find out.
Mostly, the meaning of this post is that you never know what you may encounter in Japan in any given day.