I don’t know if you’ll see this but here’s how I understand it (also following Genki).
Genki is only using one of なら’s uses and that’s to answer a question counterfactually to contrast the question and provide an indirect response which isn’t rude. They explain this as:
BunPro restate this as:
A remains the same but B is used instead of X on BunPro.
The Dictionary of Basic Japanese Grammar also say this about this way of using なら:
Again, S1 = A and S2 = X/B.
Let’s look at the examples examples.
Here we’re seeing the speaker make a counterfactual statement to contrast the question. A/S1 = チリ and X/B/S2 is 行ったことがある.
行ったことがある only applies to Chile and not Brazil.
So even though なら has more applications outside of answering questions in an indirect way, that’s the only usage you learn with Genki, just be aware that it can mean other things as well.
I hope that helped you understand this isn’t a separate grammar point, just a specific use of it!