And, then we would get into an entire conversation on their (Twain and his compatriots') idea of equal rights and Mark Twain's writings like 'Huckleberry Finn' which feature such [sarcasm]forward moving characters[/sarcasm] like Jim...whom I understand is a 'Yassuh massa...' type of character.
Mind you, I haven't actually read the book; I'm getting my info from online searches and what I've heard over the years.
Then you really need to read the book for yourself, because that's really missing the point. Yes, by today's standards, the portrayal of Jim could be seen as somewhat backward and naive, but so was the portrayal of female equality in
Star Trek, say. First steps don't go as far as later steps. Even the most racially enlightened minds of the nineteenth century would seem prejudiced by our standards; at the time, the leading debate wasn't about whether blacks were equal to whites but whether they were even truly human, so the bar was set somewhat lower.
So you have to look at a work by the standards of its time. And
Huckleberry Finn was intended to satirize and discredit the institution of slavery by portraying Jim, the escaped slave, as a good, intelligent man and a true friend to Huck. Compared to other contemporary portrayals of black people, that was very much a forward-moving character. I've never thought it was fair to condemn people for not being
as far ahead of their time as we are generations later. We couldn't have climbed higher than they did if we hadn't been building on the foundations they laid for us.
Anyway, the point is that Clemens was well-known for his involvement with the abolitionist and equal-rights movements and other social causes. Notably, the famed emancipationist Henry Huttleston Rogers became friends with Clemens in the same year "Time's Arrow" takes place. So even if Clemens and his compatriots weren't
as racially enlightened as we are, that doesn't change the fact that it's logical that they would've been the ones most likely to associate with Guinan.
(In fact, the timing of Clemens' meeting with Rogers places it shortly after "Time's Arrow," so I like to think that Guinan introduced them. The problem, however, is that the real Clemens was in Europe at the time of the episode -- a newspaper with an August 13, 1893 date is shown -- and only returned briefly to New York, where he met Rogers.)