As he said it is random but he has created rules, ie, must be contained within the triangle and must be half way to the next point, hence you end up with a contained random pattern based on a formula, where some points cannot be achieved, ie, these blank areas. Still very interesting as every point cannot be made inside the triangle,
This is essentially an academic mathematical answer, because usually Engineers have to go that step further to get something invented or working, and if told to get into that blank area, then we just use a poggle factor to suit, sometimes this is called cheating