At the end of the article, it says that if you assigned 4.3 billion people 4.3 billion IPv6 addresses each, you'd have 18 million trillion IPv6 addresses left. Actually, you'd have 18 million trillion times more addresses than you've used, which means you'd have (18 million trillion - 1) * 4.3 billion ^ 2 addresses left.

Using the notation NeM = N*10^M:

4.3e9 squared is about 18e18, which is nothing compared to the 3e38 addresses available in IPv6.

The key is that 3e38 - 18e18 still equals 1e39, not 3e38/18e18.