What does it mean if a CT of chest shows lungs are well-aerated but are moderately hyperinflation bilaterally?

Air Trapping. Lung hyperinflation on plain x-ray or ct scan is usually a sign of air trapped in the lungs of a patient with an obstructive lung disease such as asthma or copd.
Depends. Hard to say- it depends on the context of their descriptions. Hyperinflation is usually caused by obstructive small airway diseases, most commonly things such as copd, emphysema, and asthma. Things that irritate the airway and cause narrowing or "overly pliable" small airways cause air trapping, ie make it harder to exhale / ventilate.
Sign of asthma. Hyperinflation is a sign of asthma meaning the lungs are 'full' of air and literally 'trapped'. Asthma is a reversible small airway disease in which inflammation, secretions, and spasm combine to keep air from 'getting out of lungs'. Steroid (controller) inhalers are the mainstay of chronic asthma but are under-utilized by most asthma patients.