I don't know whether the vaccine helps to explain the lesser severity of MAC in your case. However, I have kept investigating and found a couple of interesting references (pdfs attached). One reports the findings in Finland where universal BCG vaccination was stopped in 2006 (Kontturi A, Soini H, Ollgren J, Salo E. Increase in Childhood Nontuberculous Mycobacterial Infections After Bacille Calmette-Guerin Coverage Drop: A Nationwide, Population-Based Retrospective Study, Finland, 1995-2016. Clin Infect Dis. 2018;67(8):1256–61), and the conclusions were "After infant BCG coverage in Finland decreased, childhood NTM infections increased drastically. As there is no other apparent cause for the increase, this indicates that BCG offers protection against childhood NTM disease. This observation adds to the understanding of childhood NTM epidemiology and might explain why the disease is emerging in some countries." The other paper is about a similar study in the Czech Republic (Trnka L, Dankova D, Svandova E. Six years’ experience with the discontinuation of BCG vaccination. 4. Protective effect of BCG vaccination against the Mycobacterium avium intracellulare complex. Tuber Lung Dis. 1994;75(5):348–52), in which the authors concluded "In non-BCG vaccinated children the incidence of lymphadenitis caused by M. avium complex was considerably higher than in vaccinated children. BCG cells possess antigenic determinants which confer protective immunity probably both against M. tuberculosis and against M. avium complex infections. It may thus be assumed that BCG vaccination protects both against pathogenic tubercle bacilli and M. avium complex. This should be taken into consideration before recommending discontinuation of mass BCG vaccination of newborns in areas with a high prevalence of M. avium complex infection."