The narrator in "A Mother in Mannville" by Marjorie K. Rawlings, describes Jerry as a boy with integrity. She describes it:
"My father had it--there is another of whom I am almost sure--but almost no man of my acquaintance possesses it with the clarity, the purity, the simplicity of a mountain stream. But the boy Jerry had it. It is bedded on courage, but it is more than brave. It is honest, but it is more than honesty." (Rawlings 4)
So, why would this boy with such an honest character lie? He has found in the narrator a mother figure-someone who he would very much like to be his mother. She is someone who listens to him, who respects him, who might even be able to love him, so Jerry tells her one day that she "looks like his mother," and from there, his story expands. He does not want this woman to think that someone could have given him up. Maybe he feels that by saying his mother is alive, the narrator will see that he is worthy of love-and especially of HER love.