Well there are some theories behind it that aims to explain the behavior. The most popular one seems to be that It's a big deal to a lot of people, and those who hold crypto are converting to fiat to prepare for it. It especially made sense back when China had one of the largest trading volumes, and it still somewhat does now because other countries like South Korea (which is a huge market) also celebrate it. It's kind of like how people were predicting Bitcoin would go down before Christmas because everyone's going to be out spending.

I'm certainly not ruling out your self-fulfilling prophecy theory though, as it does make sense. There might be people who are thinking that the market will inevitably crash because of the trend, so they decide to sell high waiting to buy low, making the prophecy go full circle.