It appears that Jiyeon has requested the song specifically from IU, her long-lasting friend who decided to sing at the wedding. Before singing, IU congratulated Jiyeon and the groom Hwang Jae Gyun with the following words:
"Jiyeon said she didn't want to cry on this day too much, so she wanted me to sing a happy song. The bride told me to sing this as if I were dancing on my feet, so I will try my best to get hyped up even though the behavior may not be entirely suitable for this occasion. You two look so good together. My friend doesn't like to cry that much, especially after inviting a lot of people with gratitude for such a beautiful wedding. So, I hope my 'brother-in-law' [the groom] can make her smile from now on. Be happy, Jiyeon."
In other news, BTS's Jin also attended the wedding, as seen in video clips taken from the ceremony.