It could but that would still be illegal. He can prohibit access if the capacity limitation would be reached, and that is not the case.
Moreover, this is also not supported by facts: the manager was observed inviting white guests.
A family gathering for a reunion is not likely to act like Jesse Jackson. And, they are not overly sensitive either: have not been offended by the name of the place, for example. Sounds to me like they just wanted to have a good time and simply ran into a racist.
Not if it was a homeowner's association owned pool, which is what it was. It was not a pool that belonged to a 'resort' as the article implies. It was private property.