Korris explained that he and his compatriots were passengers aboard the ship, en route to outpost M-Zed-5. The ship was suddenly "attacked without warning by a Ferengi cruiser" and as a result "unknowingly entered the Neutral Zone."
When it was revealed by Worf that the Ferengi had already been ruled out as the aggressors, Korris stated that "the weapons were Klingon, but the vessel was Ferengi."
Korris continued to explain that after he and his compatriots took control of the ship, he was able to destroy the cruiser, with merculite rockets, after the Ferengi called for surrender, and had lowered their shields.
It was later revealed by Korris to Worf, in confidence, that the ship was indeed not a Ferengi cruiser, but a Klingon cruiser, sent to retrieve them, for return back to Qo'noS. (TNG: "Heart of Glory")