'Unofficial trailer'(?) for Peter Callow's The Circle

What is an unofficial trailer? How does it differ from an ordinary trailer? Or a teaser? Has this been edited and posted onto YouTube without the director’s knowledge or permission? Is it some sort of weird bootleg marketing?

Who knows? Anyway, this is our first look at The Circle, directed by Peter Callow, which was filmed in Essex and Cambridgeshire in September. The cast includes Emily Yarrow, Eva-Marie Kung and Sesselia Olafs, who posted the trailer.

“A University professor takes four archaeology students on a field trip to a remote Scottish island. With tensions already present in the group, they unearth clues to an ancient mystery that will threaten their lives.”