Yeah i thought something like that too but who knows what they have thought through.. for all we know .. how do we know that those things that happend on Sulaco really was what Bishop last said to Ripley, after all .. he was controlled and produced by the Weyland company!
Maybe "someone" docked with Sulaco and planted something there to shut Ripley and the other survivors up .. but i dont know really, looking forward to seeing what they have mixxed up for us