Actually a JW can have human hemoglobin
Yes, I believe this is true. Haemoglobin is actually a secondary blood fraction, according to Watchtower classification of blood products. So JWs can have haemoglobin if their conscience permits it. That particular JW is unaware of this, or his conscience does not permit him to have it, and, he is unaware of the fact that hemopure is basically just the animal version of the same haemoglobin he is refusing.
However, it's rather foolish that red blood cells are banned while haemoglobin - the thing that makes a red blood cell a red blood cell - isn't considered a primary blood fraction and isn't banned. To throw the JWs' alcohol analogy back in their faces in the proper way: It's as foolish as if you went to your doctor and he told you to abstain from alcoholic beverages, but told you that you can have pure ethanol injected in your veins because it's not an alcoholic beverage but a fraction thereof.