Harry pretended he put felix felicis on his drink
Cuz by ron thinking that he was lucky, he unlocked his true potential in quidditch
He felt that luck was on his side. On top of that even Hermione said that Harry added, which was false. Ron had never tasted felis. So these factors made ron believe that Harry added into his pumpkin 🎃juice
Ron was a great Quidditch player (opinion), he just lacked confidence. That lack of confidence really affected his ability to play. He thought Felix Felicis in his drink, so he thought he was lucky. Him thinking he was lucky kinda helped him get over his nervousness and gain some confidence. It doesn’t matter if he did or didn’t have Felix Felicis, he thought he did and that helped him.
Actually, lack of confidence is the real cause for MANNYY problems
They just asked for Quidditch not Ron’s fatal flaw.