Yes that's true. They sold 60m Yowies in one year and were the highest selling kids book in Aust. They sold pencil cases, school bags, pillow cases, t-shirts...you name it. They were an Aussie brand which is why they are still remembered here.
Can they do it again though without the might of Cadbury behind them? They outsold Kinder 3 : 1
They currently sell 13 m globally. Kinder sell 4 billion.