Pre-flood Rock Monsters? Modern Noah Mythology? How did the "Noah" movie decide to include rock monsters depicted as fallen angels? (helping him, nonetheless!)

This is one of many, many biblical deviations the movie makes, but I'm curious what traditional sources are bastardizing the story so badly? Or is it just the creativity of modern man gone unrestrained?
As the producer of the movie said when asked about inaccuracies in the movie "It is entertainment and not a documentary."

Biblical movies, down through their history, have injected some parts for entertainment into their story line. Even the best made Biblical movies, such Charlton Heston's great movie about Moses, included a love triangle involving Joshua that is not a part of the Bible.

It appears that whether wittingly or unwittingly, Hollywood has deviated from known Scripture in increasingly greater ways, that the Stories from the Bible have been altered in the mind of the public.

Whether intentional or not this process has slowly had a negative impact on the public's perception of the veracity of the Bible.

Many devout Christians have attributed this process to Satan, and there may be more truth to that than meets the eye. However, it must be assumed that it was not a conscious effort on the part of the movie makers to distort the perceptions of the Bible but to satisfy the hunger of the public for increasingly exciting entertainment.

That process is not just reserved for Biblical interpretation in movies, but extends to all movies. Beginning back in the 70's with movies, such as where the girl's head spun around on her body, to as you remarked, the depiction of fallen Angels as Rock monsters. Christianity has been rapidly denigrated by Hollywood.

Sadly the depiction of fallen Angels helping Noah, (I have to take your word for that, since I have not seen this movie and never will because I am blind); will give some the idea that Fallen Angels can be good, which is contradictory to the Bible, since the fallen Angels are Satan's demons, and are evil. 

One of the first Bible epics, which I still occasionally watch, deviated from the Biblical account of Jesus' crucifixion in that in the Bible Roman soldiers cast lots for Jesus' garments, but in the movie that was not shown.

You can make your own determination as to whether or not this is the work of Satan or not, for myself I can only say that it has had a negative effect on Christianity.