I would agree that he is 50% white. But "Arab" is an ethnicity, not a racial group. More to the point, if you have seen photos of Barack Obama Sr., the purported father, you have to come to the conclusion that Sr. is 100% Black. Therefore, Barry would have to be classified as 50% white, 50% Black.
Of course, it is possible that a sloppy clerical error was made on the original BC, perhaps assuming, wrongly, that if the mother is Caucasian, the child is Caucasian. Mixed race black-white babies weren't common at the time, even in Hawaii (regardless of where he was actually born), so that is a possibility, though a remote one.
Still, more likely than your suggestion that the original BC showed the baby's race as "Caucasian" is the possibility that it showed the father to be "Unknown" or someone other than Barack Sr. That would be even more embarrassing to Barry. But the most harmful would still be a BC that showed the place of birth as Kenya, because that would wipe out any notion that he is constitutionally qualified to be POTUS.
I have been disabused of that makeup, rightly so. But you got my point . Something smells!