The most popular belief is that it was caused by a sudden and mysterious rise of demand in China. They base their assumption on the high volume that BTCChina showed during that time, while ignoring the fact that Chinese exchanges have the habit of faking volume.
The pump upwards was fueled by MtGox and BTCChina's volume was created only as a misdirection. BTCChina volume was only created to explain this sudden rise in demand and to hide the fact that the price is mainly pumped by Karpeles and his non existent money. Karpeles thought that he can pump bitcoin enough to start a rise that would make him back the coins that were lost by the previous hack. It backfired of a simple reason - Karpeles is a terrible trader. He was outplayed even by the majority, so his losses got even bigger in both coin and fiat. Most of the smart traders just profited from this pump and got out at the right time. Only the inexperienced get-rich-quick folks were the ones who didn't know the right time when to get out, but their investments were small and meaningless anyway.

I think that the bitcoin scenery is amusing because people are still in strong denial about the whole 2013 pump situation. Miners are still holding their high production cost coin because "any minute now, another mysterious and unexplained pump will surely come". But it won't come if no one is orchestrating a similar fraud.
The coming of Gemini is finally dissolving this myth that institutional investors are waiting for the right chance to be the greater fools of bitcoin. I think that this myth will now be more in the form of "ETF will change everything!".
So, to me, it's not a question if the bitcoin price will face a total collapse, but only when will it happen.
When will all the illusions of bitcoins worth finally fade. When people will finally realize that artificial scarcity doesn't work with something that is easily replaceable, and the network effect of bitcoin is mostly dependent on a bad brand name. That the future of crypto is not about them getting easy riches, but about better technological solutions that have addressed the problems that have kept bitcoin from being a practical tool of finance.