To what extent is it true that the meeting of a pure wet substance with an impure dry substance does not render it impure, and the meeting of an impure wet substance with a pure dry substance does not render it impure?

The fatwa concerning touching a child's hand soiled with urine after it has dried means that impurity does not transfer to a dry garment if it is touched by a dry hand. This is based on the rule that if an impure object meets a pure object, and both are dry, the pure object does not become impure. However, if one of them is wet, the impurity affects the other. Therefore, the questioner's understanding of the fatwa is incorrect.