Where can I find a source for your first point? This site[1] mentions this test as a way to detect adulteration by artificial coloring in turmeric powder, not adulteration by lead.
I think the point (at least the one I gathered from the article) is that turmeric is sometimes artificially colored to make it the right shade of yellow, and that lead is in the chemical often used for that coloring. Thus, evidence of artificial coloring is a heuristic for presence of lead.
I suppose your turmeric could fail the test, and you could decide that the failure is not a sufficient proof of lead presence, because it might be a different lead-free artificial coloring that caused the test failure. That is absolutely your right to decide.
I suppose your turmeric could fail the test, and you could decide that the failure is not a sufficient proof of lead presence, because it might be a different lead-free artificial coloring that caused the test failure. That is absolutely your right to decide.