A 35-year-old male patient is scheduled for emergency laparotomy following a stab wound to the abdomen. Induction is planned with propofol and a muscle relaxant. The patient has a history of severe burns 6 months ago affecting 40% of his body surface area, now in the healing phase. During intubation, after administration of succinylcholine 1.5 mg/kg IV, the patient develops severe hyperkalemia (K⁺ 7.2 mEq/L), peaked T waves on ECG, and cardiac arrhythmias. What is the most likely explanation for this complication?