https://www.theatlantic.com/notes/2015/08/toni-morrison-wasnt-giving-bill-clinton-a-compliment/402517/
This is almost always what people refer to when they talk about "first black president" outside the context of Obama, so when you vaguely referred to it I thought you meant that.
Your admonition to me to "Google" is not exactly helping. Are you talking about John Hanson, or about any of the other U.S. presidents who possibly had a bit of Negro ancestry in their blood? (This was one of the first Google hits: https://fookembug.wordpress.com/2008/12/01/the-seven-black-presidents-before-barack-obama/)
If it's John Hanson, it appears he served as "president" under the Articles of Confederation before the U.S. Constitution was adopted and Article II created the office of President as we know it today. This is indeed an interesting factoid that I was never taught in school, but I don't think it overturns Obama's historic achievement, and it does not totally re-shape my worldview. Same goes for the other U.S. presidents with possible claims of Negro heritage -- I do not doubt that all of them were basically white for all intents and purposes.
Heck, I may even have Negro heritage myself, since my Dad was adopted and does not know his birth parents. But: it's pretty clear just looking at me that I'm white, and that's how I identify as in public and online and is the way I answer on all my government forms.
Not to take away at all from your experience living in a very diverse neighborhood. But, most places I've been in America and certainly in the city in which I live, racial categories are a lot starker.