3m lead test confusion
It most likely means you have lead paint underneath a coat of latex paint. In places where’s there’s a crack in the latex, the tester  is responding to the lead. 

If there’s no small children and the paint isn’t peeling, it’s often best to keep the lead in place by putting another coat of latex paint on top, sealing it. Trying to remove the lead by sanding or chemical means can often be more toxic than removal in these situations. 

If there are small children and/or the paint is peeling, you may want to refer to a lead specialist for the best mitigation for these circumstances.