K I must have missed this plot entirely, darn interpretive films
The key is in the aspect ratio. The screen gets narrower when it's the fan's perspective 
In the beginning of the video where things are real (wider aspect ratio), you see two members getting close and touching each other, but they're just planning choreography. You see one member pretending to feed another and then teasingly taking the snack back. You see two members sharing ear buds to watch something on a phone. All of these are pretty normal and easy to see as platonic.
But then later from the fan's perspective (narrower aspect ratio), these scenarios are repeated in much more romantic seeming ways, and at the same time there are moments where it's like the members are flirting with the fan or treating the fan like a friend or a younger sibling, so there's a weird parasocial component in the mix too. Then by the end of the video the more romantic versions of things have taken on the wider aspect ratio, and the fan's perspective has also, meaning the fan's fantasy has basically become reality (at least to the fan).
Well if I search it and it looks… not so good, I’m probably not going to read it because I’m picky
A reasonable approach 
You are right ? I was too tired and didn’t see that it’s a woman.
Well that solves that mystery 
