The theory was posted by blogger freyr25, who saw the MV and thought it was very much referring to the Sewol tragedy. The theory went viral, getting not only a bunch of views and comments, but also getting posted over Korea's portal sites.
The first 'proof' were the paper boats featured in the teaser. The paper boats were one of the symbols of the mourning after the Sewol incident.
Yeri is the only one blurred out on the album cover. Yeri, who is 18 this year, is the same age as most of the victims of the Sewol ferry incident at the time of the accident.
At the beginning of the MV, the girls get all dolled up in preparation for their trip. Behind Yeri, especially, is a yellow butterfly that symbolizes hope. (Yellow is also the color for the Sewol ferry ribbon.) However, all the girls have dark expressions even when getting their makeup done, supposedly foreboding the tragedy that's to come.
The set looks like the inside of a boat more than a hotel/motel, especially because of the lights used.
The sign that can be seen in the background seems to read 'AIS on 15-16'. The AIS, or the Automatic Identification System, is an automatic tracking system used on ships and by vessel traffic services (VTS) for identifying and locating vessels. The Sewol AIS was suspected to be turned off between the 15th and 16th.
Seulgi looks into the keyhole, learning the truth. Her looking at the camera supposedly symbolizes that she realizes the truth, and later she tries to leave, but is blocked by water all around her, symbolizing all the students that could have been saved.
Irene, who sits still, symbolizes the students who listened as they were told to just stay still. Joy, who is the sole survivor as we'll see later, watches her sadly as Irene just sits still from outside the window.
Irene, who has her eyes covered, doesn't know the truth (which is why she was just sitting still.)
Joy on the other hand, climbs the ladder and leaves, succeeding in escaping. She's wearing yellow - the symbol of hope and the color of the Sewol ferry ribbon.
Seulgi, who knows the truth, opens the window for Wendy, but it's too late as Wendy's already soaked. Seulgi cries when she sees this.
Yeri is sound asleep on a boat that's starting to fill with water.
When they're all together, the screen is light.
However, the screen changes to just Joy, the sole survivor, alone in the dark. The lyrics that play at this moment is 'Let's meet again'.
Seulgi, who could have escaped because she knew the truth, fails as the halls of the 'boat' fill up with water. She opens the door to heaven, where the other members (except Joy) are waiting for her dressed in white.
Wendy escapes the dripping water by going under a table. The students in the Sewol ferry, as a last resort to try to stay safe, crawled under tables.
This scene under the aurora is said to be a fantasy where all 5 members can be together.
Candles are used not only to symbolize hope but also to pay respects.
Yeri finally wakes, but is already soaked and her boat sinks under bloody water.
Water pours into the boat through the window, shocking Irene.
She falls into a room filled with water (blue, with furniture floating). A thing to note here is that the black underneath is tilted, implying that Irene's floor is actually tilted like the Sewol ferry was.
Joy, the sole survivor, wears black to pay respects.
There's an emergency bell, and the door up front has no door handle on the inside - signifying it can't be opened from the inside.
The last remaining light symbolizes the last hope for the students still trapped inside.
The background of the teaser is the black sea. Also, the theory supposes that the moon behind the cloud signifies the lunar calendar... which would connect to the lunar date of the Sewol ferry sinking - March 17th. This would match up with why SM suddenly delayed Red Velvet's comeback a day, even if they cited other problems.
The theory seems to find some support in that SM Entertainment had a Sewol song before in f(x)'s "Red Light", which was officially confirmed to be referring to the tragedy.
What do you think? Are these too far-fetched, or does it make sense?