They see every order on their books. In other words..if your order was routed to them, they would see your order as well everyone elses with similar orders.

If you placed your order using common text book criteria you can be assured you and piles of other folks all had stops at the same levels that were an easy target.

Once they get the stock up down enough to trigger all the stops they can simply use the sell orders to jam the stock down further, then"plug" the tail end of what are now mostly all stops that triggered market orders...then  fade away and bid it up once they have filled them all at the lows.