Bitcoin market could definitely be manipulated by anyone but in order to do that you require a great amount of money and a good reason to do that. You can't just play with the price because you are bored and don't have anything else to do, you do it with a certain reason and purpose.
Whales could actually cause this to happen but they might no longer succeed because we have lots of investors who are actually quite very rich and genuine to counter the actions of the whales with their simple act, some of the actions of these genuine investors are what we saw yesterday which got the price stabilized above $4500, so right now, with the way bitcoin is being accepted and used, it will surely be quite difficult for them to really move that market again as they like, and even if they will do, their effect on the market will really be less significant and will seems just like that of traders activities.