Final answer:
Small red papules with white centers in the buccal mucosa of a 16-year-old male are indicative of Koplik's spots, which are a diagnostic sign of measles.
Step-by-step explanation:
A 16-year-old male presenting with small-sized red papules with white centers inside the buccal mucosa by the lower molars is likely showing signs of Koplik's spots. Koplik's spots are a hallmark sign of measles, often appearing in the mouth before the typical measles skin rash develops. This indication derives from the clinical diagnosis of measles, characterized by the distinct oral presentation as well as a raised macular rash that starts on the face and spreads to the extremities.