I've known about this verse for a while -- the funny thing is that it appears in the version of "Hakuna Matata" on the Rhythm of the Pride Lands CD instead of Pumbaa's verse. Also, in the TLK comic, when Timon and Pumbaa first meet Simba and start telling him about their way of life, Timon makes a speech that is obviously a shortened version of his verse.
Simba wrote:well, if they had added this we wouldn't have TLK1.5 to explain where Timon came from.
Timon actually has two other origin stories in the Timon and Pumbaa Show (banished from his colony for letting a snake attack while he was on guard duty) and The Lion King: A Nature Fun and Learn Series (an eagle attacks his colony but no one heeds his warning about it because before that event, he was constantly raising the alarm when there was no danger [think "The Boy Who Cried Wolf"]) -- three different origin stories, and they just had to throw one more on the pile...