It's not found footage. It is one of the best teaser trailers I've seen in a long time though.
The movie was originally not connected to Cloverfield at all until JJ became a producer on it.
The early plot description when it was going by The Cellar/Valencia:
"The story follows a young woman who wakes up in a cellar after a severe car accident and fears she has been abducted. Her captor, a doomsday prepper, tells her he saved her life and that there has been a terrible chemical attack that has left the outside uninhabitable. She does not know what to believe and as tensions rise, she decides she must escape, regardless of the terrors that await outside.”