It's an antibody against phospholipids that interferes with the test but makes platelets hypercoaguable.
Remember, the PT and PTT tests work by putting in parts of the coagulation pathway and letting the patient's serum complete the pathway. With lupus anticoagulant antibodies, those antibodies artificially increase these times by interfering with components of the test. It's purely an artifact though since the antibodies, in vivo, actually make the patient's platelets more likely to coagulate, not less. The platelet membrane is part of the intrinsic pathway, which involves fixing Xase on the platelet membrane via vWF+F8.