That was a joke. Let me tell you the reason why it is funny...
Why was 6 afraid of 7?
Q: Why was 6 afraid of 7? A: Because 7, 8, 9.
This joke is also fairly common. The core of this joke is the fact that 8 is a homophone for ate. The reader hears both the sequence of numbers as well as the words seven ate nine at the same time. If you didn't guess it yet, this is a pun.