Since that didn't happen, you'll be waiting for a long time.....
The pilots didn't see the craft drop, it was reported from another ship's radar which was probably malfunctioning or picking-up erroneous readings.
Drones don't need windows and since we don't know how far away the object was from the fighters, it escaping them would just be a matter of turning faster than they could and it's relative size is based on judgement without a good frame of reference. Without human pilots, drones are capable of performing maneuvers that would hurt/kill a human being. The object making 'erratic movements' is characteristic of drone flight using propellers for propulsion so, no wings or exhaust plume.
I'm just saying, there's better explanations than 'It wuz alienz!!!'