Classical "bot" trading, or algorithmic trading.This implies one...

Classical "bot" trading, or algorithmic trading.

This implies one or more of the big brokers is accumulating. It is only brokers who can do this style of programmed trading, as the brokerage fees would make this impractical for the rest of us. Brokers, of course, don't have to pay themselves brokerage!

They could be doing this for their own trading account, or they may be doing it on behalf of a client who want to accumulate a sizeable parcel.