Your concerns and questions are legitimate. An experienced radiologist who specializes in the chest can often distinguish between the CT changes of these two diseases. Both of these diseases may remain stable, sometimes for considerable periods of time. So this would not help you to know which might be the problem.
Hilar adenopathy is common with sarcoid and seldom seen with idiopathic pulmonary fibrosis (IPF). Adenopathy is another term for enlarged lymph nodes. In fact, enlargement of the hilar lymph nodes is the most common finding when sarcoid affects the lungs. The lung hilar is the area at the center of the lungs near the heart.
If the changes on the chest CT scan cleared quickly, especially after taking steroids, this would favor sarcoid. Sarcoid is relatively easy to diagnose by endobronchial or transbronchial biopsy. Your husband may have had this done when he had the bronchoscopy. With the bronchoscope tiny pieces of lung tissue can be taken for further testing. An open lung biopsy is not always needed.
You should raise your questions with your husband's doctor. Also attempt to ascertain the degree of certainty with which the diagnosis of IPF has been made. Please read our Interstitial Lung Disease MedFact at http://www.nationaljewish.org/medfacts/interstitial.html and our Sarcoidosis MedFact at http://www.nationaljewish.org/medfacts/sarcoid.html for more information on each of these diseases.