The man was indeed a Black man, according to the laws of the time, as all of the various Booker T. Washington Cemeteries from Louisiana to Illinois were for Black people. But, under the law prevailing even much later (which said any Black blood made you "Black"), we would all be listed as Black:

However, just what constitutes "being black?" Since the human genome project and all the other genetic work of the past several years, we now know, scientifically speaking, that the average "White Man" in the U.S. of European descent has on average the equivalent of one Black ancestor per each 256 ancestors (And we have, of course, millions of ancestors.) It may be one quarter here, one half Black ancestor there, etc., but still averages out one "Whole" Black per every 256 ancestors. Some Blacks were, of course, "Passing" as Whites.

Booker T. Washington Cemetery

http://www.stclair-ilgs.org/booker.htm