On that same day, Taeyang posted a picture of his manager on Instagram; the same manager that appeared in the photos released by Dispatch of G-Dragon and Kiko Mizuhara on their date in Seoul. This is probably the hyung that the eyewitness identified in their comment.
After some research, it was discovered that the restaurant where Taeyang and Min Hyorin were spotted by the netizen was the same restaurant pictured in Taeyang’s Instagram photo (as seen below).