Apparently Sisko was a student of history. What he said about Las Vegas of that era was more or less accurate. He didn't want to play pretend and pretend that segregation didn't exist at that time. That didn't seem unreasonable. It may be questionable whether a 24th century person would get so upset about it. But Sisko was a passionate person. He seemed to have a passion for African culture. He was also passionate about creole cuisine. And he had a love for baseball and baseball history even though professional baseball went extinct centuries ago. A 24th century man having a passion for baseball. Odd or not. Sisko's wording may have been out of the ordinary, but his pointing out that particular fact of Vegas history seemed reasonable.