Bitcoin is supposed to be free of any control but it seems like a few people have more control over it than others ... which is a huge drawback of Bitcoin in that case.
That freedom also permits people to accumulate vast amounts.
You don't have to have vast amounts to have a strong influence over one strong price movement. This market is currently so weedy that the majority are looking for others to make a move to follow, and the rest will be bots that pile in to whatever is sparked.
You could throw away a few thousand coins at provoking a plunge but if the price goes down and stays down then that's looking like the 'true' price to me. No one can keep a price down for more than a few hours artificially.