That was a joke. Let me tell you the reason why it is funny...
What's the difference between a hippo and a Zippo?
What's the difference between a hippo and a Zippo? One's really heavy and the other's a little lighter.
This is a pun. "A little lighter" could mean "a small device for starting fires", or "a small amount less heavy". The humor derived from this joke comes from the listener recognizing that the joke has both of those meanings.