I was tested positive for ppd, but had the bcg vac, how is this possible?

BCG: This is an attenuated tuberculosis vaccine that gives so-so protection but does not render you proof against tb. It can itself make you have a positive ppd. Governments may require you to be treated for TB on the basis of this alone which is regrettable. Or you have have met the tubercle bacillus and beaten it, or have tb, either of which is likely to make your PPD positive.