Of course, Kiefer's love for Quidditch was known by every single person attending Hogwarts. But his love for watermelon? Less than suspected. The brunet spent his whole summer doing the same things repeatedly: practising, talking about Quidditch and eventually eating a whole watermelon by himself. And that was the only way of keeping his mouth shut about Quidditch for five minutes.
By giving him a whole watermelon.
So when he saw the watermelon on the table, the wizard was beaming with excitement. Kiefer went to visit you, straining a bit from his habits, so the fruit felt like a reward.
And now there he was, sitting at your garden's table, cutting the fruit as if he'd done that his whole life before eventually handing you a piece of the watermelon. Although it looked like it pained him deeply. As if you weren't the one who bought the fruit in the first place.