This child reminds me of our nephew - he was diagnosed with PDD-NOS - a high-functioning form of autism. I really think it is time for this parent to seek medical advice. I wish you the best ...
Then thats all you can do as he is not your child ,you obviosly care and have pointed it out to his Mom the rest is up to her, it could be normal childnood behavior children like to spin, if she was concerned she could ask her Doctor for advice, do you think he hears you ,when you say he doesnt follow instructions, you could ask his Mom to get his hearing checked out.