Surely if his parents were either patriots or military they would have known that the general's name was not McAuthur.
They might have as a pun, or an homage. Like a patriotic spanish-speaking family named "Arbusto" (Bush) naming their kid "Jorge Walker Arbusto". It's not the best example, but it's all the time I will dedicate to this post at this point.
And by the way, since when does proper spelling mean anything to certain demographics when naming their kids?