Assuming this is based on tracked addresses, a whale address would be an address connected to a certain a amount of bitcoin? The question is, how do we know these addresses do not belong to groups (exchange, etf etc)? This message implies there are lone buyers buying a lot, while it could also mean ...

Since it was mostly ETFs selling I think it's institutions readjusting to their target percentage allocations and some selling in preparation for tax season for others.