Maybe he donated to a US hospital because he couldn't find anyone outside of the USA who wanted US$. :-)
More seriously, the quality of health care available to Americans without health insurance is comparable to that in many third world countries; so funding US hospitals (which provide a disproportionate amount of their services to the uninsured, who often don't seek treatment for medical issues until said issues become life-threatening) can be seen as providing assistance to the disadvantages.
Finally -- as other people have said, it was his money. Up to him to decide what to do with it.
More seriously, the quality of health care available to Americans without health insurance is comparable to that in many third world countries; so funding US hospitals (which provide a disproportionate amount of their services to the uninsured, who often don't seek treatment for medical issues until said issues become life-threatening) can be seen as providing assistance to the disadvantages.
Finally -- as other people have said, it was his money. Up to him to decide what to do with it.