A 44-year-old man with acute eosinophilic pneumonia is ventilated for severe hypoxaemia. CT chest shows diffuse bilateral ground-glass opacities. BAL shows >40% eosinophils. He is started on high-dose IV methylprednisolone. Within 24 hours, his oxygenation dramatically improves. What distinguishes this condition from typical ARDS in terms of treatment response?