Honestly though her advice isn't awful, it's a pretty good way to get someone's attention before starting to get serious. The friend just isn't aware that both our MCs are already super into each other so she's advising for the hunt unaware the prey is already willing
That's still awful advice, though?! They literally just had a successful date, held hands the entire time, and even interlocked their fingers. He's already thinking about her, and she's obviously thinking about him too. She already has his attention. So what does her friend tell her to do? Pull back and make him wonder if he was imagining her interest so he'll keep thinking about her. Seriously? Why deliberately make someone question whether you like them when things were already progressing perfectly fine?
And yes, that can absolutely backfire. Not everyone (it's strange that people still does that at all) is going to go, "Oh my God, maybe she likes me after all, I need to chase her!" Some people are just going to think they misread the situation, that they did something wrong, or that she's no longer interested, and pull away. If you like someone and things are already going well, why the hell would you start playing these stupid push-and-pull games? Just be honest. Being sincere about your feelings isn't some weak move that makes the other person lose interest. And even if it does, then honestly, that's probably for the best. It might hurt at first, but it's better to move on than to keep playing games just to keep someone interested.