You have to know the following basics:
I think you might mean lung TB. Although TB is an infectious disease, it does not mean everyone diagnosed with TB is contagious. If the patient could cough up TB bacteria, then the patient is contagious. If the TB patient does not cough up TB bacteria, then the patient is not contagious despite that the patient is diagnosed with TB.
A test for sputum TB bacteria is a commonly used test to determine whether the patient could cough up TB bacteria and thus whether contagious.
Thus the answer to your question is it depends.
However, for assurance, it is better for your son to get isolated and treated with anti-TB meds. It usually takes about 6 months to cure TB.