I can't say what it is exactly, but if I have to guess, I would say it's just profit taking.
Bitcoin has been low for a while, so now that Bitcoin has gone up, it's normal for some people to take profit, especially ETF guys that are not really in the long term business. They need the short term profit. It's normal.
This is indeed a fluctuation, but it made me think about something, namely the topic of ETF outflows: We can see how many different hacks are currently taking place using artificial intelligence and social engineering, and recently I started thinking that perhaps the next target for hackers will be the custodial services of Bitcoin ETFs. And realizing this, those ETF investors (who neglected their own custody) decided to withdraw their assets from these companies.
It's not like the situation you're describing is impossible; it's possible that ETF companies can be hacked and all, but it's not really practical.
There have been a lot of hacks, that is for sure, but nothing about those hacks has raised the panic level enough for people to want to take their funds out of ETFs.
I don't believe there are people who are above being hacked, anybody can get hacked, including banks, but I don't see people take their money out of banks for fear of being hacked. This is because nothing has shown that their money is at risk of being stolen through a hack on the bank.
So, I don't agree with your theory.