Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is causing a massive outbreak throughout the world. In this period, diseases other than coronavirus disease (COVID-19) have not disappeared; however, it is hard for doctors to diagnose diseases that can mimic the clinical, radiological, and laboratory features of COVID-19, especially rare lung diseases such as acute eosinophilic pneumonia (AEP). We report the clinical case of a young patient who presented to the Emergency Department with respiratory failure and clinical symptoms, radiological aspects, and blood tests compatible with COVID-19; two swabs and a serology test for SARS-CoV-2 were performed, both resulted negative, but the respiratory failure worsened. Peripheral eosinophilia guided us to consider the possibility of a rare disease such as AEP, even if radiology findings were not pathognomonic. Therefore, we decided to perform a flexible bronchoscopy with bronchoalveolar lavage (BAL) at the lingula, which showed the presence of eosinophilia greater than 40%. As a consequence, we treated the patient with high-dose corticosteroids that completely resolved the respiratory symptoms. This case report highlights the difficulty of making alternative diagnoses during the COVID-19 pandemic, especially for rare lung diseases such as AEP, which may have initial characteristics similar to COVID-19.