According to this post (OP is the owner; posted yest 5/19) Yunho and BoA went to a meat restaurant Wu Dang Um Yoonsung 1964 우당 엄윤성1964 at Cheongdam

Restaurant details:

Wu Dang Um Yoosung 1964 우당엄윤성1964 (출처 : 네이버 통합검색) http://naver.me/xvFPMLiN  Apgujeong Rodeo station, exit 4 (12 mins)

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Credits:

yoonsung0707: here via @YHCM0618_WITHU,
Translated by @snxy,
Shared by TVXQ! Express