It may be they bought and sold back and forth rapidly and the unsettled trades are considered on margin even if it was mostly netted out in and out of the same

It may be they bought and sold back and forth rapidly and the unsettled trades are considered on margin even if it was mostly netted out in and out of the same stock. Doing it without settlement itself is similar to naked shorting, because while it should all net out, trades can bust, especially in a short squeeze where people's long positions have been loaned out.