Good to have some consensus on this.
Still, that line may actually be true for Li: that he cannot be defeated - if he is Gu Long's #1 fighter, that is. There are indeed some who are convinced he is or is near. Another evidence they use is in Full Moon Curved Sabre, Ding Peng said Xie Xiaofeng did not dare to oppose/challenge Li's disciples, both glorifying the awesome reputation of Li's lineage AND implying even Li's disciples >= Xie Xiaofeng.
By the way, that description (in FMCS) made Li seem like an organized crime boss; hearing his name makes one tremble and no one dares challenge his descendants.
That does make sense: Chu Liuxiang was written after Little Li, and perhaps by then Gu Long had further developed his Confidence-Righteousness Card.One interesting note I found while perusing Chu Liuxiang for examples, it turns out the famous pirate was also powered by righteousness... Whereas we are told 2nd hand about Li's righteousness, Chu Liuxiang actually states HIMSELF that because he has never committed evil, that he is confident that he will never lose!