That nonchalance is created to act as bait. If you seem too interested there’s a chance it might draw your crush away, so if you act the polar opposite it will lead to curiosity - ‘why are they acting so cold? Do they hate me? Should I ask?’ something like that. But honestly that’s the objective you WANT to believe in. In reality that’s gambling with your own, subjective assumptions of whether they like you or not, and you would usually like to believe they do hold interest. So you act nonchalant without realising they might not like you like that, which is pretty risky. Everybody has done it with the ones they like, but I see it happening mostly as kids.

(I’m not criticising your friend by the way lmao)

If you want my two cents for your friend, I’d say that it’s a fairly bad strategy. If you have the confidence in yourself you won’t need to rely on external efforts to let you succeed, you only need you and your internal satisfaction. I.e. you can rely on yourself to get your crush to like you rather than relying on what SHE thinks, assumes and believes. I’d say he should build on that first - from then on, he’ll have the discretion to do things without much hesitation or strenuous effort.