That's the bad thing about OTC. There is no general ledger. Banks are divided into hundreds of investment vehicles. If they Bitcoin buy, then certainly not in their own name. Only if it fits in with their strategy. That must have been a very big whale that can sell off 50% of the market capitalization. I believe that using the word "whale" means that someone can not explain who is behind it. I just read both articles and I think it's a plausible scenario.
A few days ago I was reading an investigative article on Cum-Ex business of the banks. Anyone who believes that banks regulate their business and only do good business is wrong. The problem is that they are already in government. It's a sad world.