The BBC article says "Every time the game is played, a reliably navigable maze is pumped out. Were the table’s values random or even slightly different, the maze would likely fail to be drawn with a playable path through it." <- the example in fig 5 IS in principle playable - the point I think is that the maze is not drawn in a way that would leave a player stumped even if they had a make-break at their disposal. i.e. Endless wall in the way.