I'm not one to acknowledge a kpop fan, unless I feel like it. It really depends on the artist or the circumstances. I don't expect friendship from it either.
I had a roommate in college that was into kpop, but she was really shy so I didn't pry. I knew she liked it because I heard her playing it in our kitchen (maybe she thought no one was home). I always caught her playing Zion.T so I would just acknowledge that I liked the song, she'd smile then drop her head, then I go on about my day.
Another girl I danced with was trying to show me a Beyonce song we should dance to. Afterwards she accidentally started playing Ring Ding Dong, and she looked horrified as she paused it. So to make sure she wasn't too embarrassed I started singing the song, and she was surprised and excited that I knew it.