I believe the father’s race was stated as “African”, not “black” as you are indicating. That is even more revealing to it being a forgery since the race back in that time frame should has stated Negro, as you point out. Whoever created this forgery just couldn’t overcome their need to use a more modern politically correct “woke-speak” term for the father’s race. African is not a race. There are many different races living in Africa. Again, another “tell” that this computer generated PDF document was a recently made forgery.
The statistic reported to the government would have been “Negro,” but that didn’t mean “African” couldn’t have been on the birth certificate if it was the answer the mother gave. This was Hawaii, where “Chinese,” “Japanese,” “Filipino,” “Korean,” “Porto Rican,” and other “races” appeared on birth certificates. In 1961 there were reasons why a mother or her parents would prefer to use the word “African,” rather than “Negro,” and a hospital clerk might well have gone along with that.