Family Mystery - WWII prisoner portrait

Hal Pufall 1945, painted by a 'German POW'

I've been meaning for some years to photograph, clean up, and post this painting.  This is a painting of my paternal grandfather Hal Pufall.  Hal fought in WWII and returned with this painting.  The story goes (this is second hand for me) that the painting was made by 'a German POW'.  Other than that I don't have much to go on.  Hal like many who fought in WWII [does] did not speak much about his time in the service.  When he did it was always about daily life and never about combat or what he saw.  So no [clues] more clues there.  We are however currently in the process of requesting his service record.

My suspicion is that this painting was actually done by holocaust camp survivor.  This suspicion is based on three clues: Stein (the painter who signed it) is a very common German/Jewish name, there is a similar story and remarkably similar painting from another GI whose painting comes from a concentration camp survivor, and the date of 1945 matches the date for the camp liberation in the aforementioned story.  Once we have a copy of his records I will be able confirm suspicions one way or the other.

Ultimately I would like to find the survivor or more likely their next of kin and pass on the story to them.  I would also like to make a portrait of them in return.