It just never ceases to amaze me how horrible people can be to God's innocent creatures
All that I can think of is that it is contagious to humans so hopefully however let him get into that condition has caught the ringworm too.
Be careful so that you do not spread it to your own family and pups. It's hard to get rid of since it can be passed back and forth very easily.
I'm so happy that he is now safe and in your care. Thank you for fostering and helping to bring him safely into your care.