Imagine 3 whales with 1000 btc each decide to sell bitcoin and by chance they do so at the same time. Of course the price will tank and people will wonder why, bots will follow and so on.
I guess you don't need to imagine as the last recent massive spike last April 2 was due to one big whale who traded long for US$100 million. And it was spread across three exchanges, to have this maximum impact. And we all know what happens next, it triggered the start of a bullish run up to this point.
But I don't think that whales really collude which each other to bring the price up (and down). Those whales really know how to play this game. But the question is how average Joes like you and me will react to this kind of news.