All the information the teaser gives away is that the song title is "Shaking", that the MV will be released on October 10th, and the full song will be out on October 14th. There's no mention of who the artist for the song is.
However, FNC Entertainment did give a tiny clue - that the artist was having a 'comeback'! In their tweet, they said, "Noon today, an INST TEASER has been surprisingly revealed on the FNC Entertainment official homepage. Which artist will have their comeback after F.T. Island? You'll see the answer at noon on October 1st on our official homepage."