There are multiple different sects of the “Black Hebrew Israelite” movement, which began in the late decades of the 19th century. Generally you can tell them appart from their choice of bedsheet vs. pleather robes and tinfoil vs rhinestone adornments. They base their theology off of a rejection of Christianity as a “white man’s religion” and Islam as “of the devil”, leaving Judaism as the default choice of a group that wishes to make converst in a community that still holds the bible to be the word of god. They draw on the traditional identification of black Americans with the plight of the Israelite slaves in Exodus, as well as a few verses about people being bound in servitude and being transported in ships. They also have a near-astrological system of associating different populations of black people in the Americas with different “lost tribes” of Israel.
Like most fledgling religions, the Black Hebrews have been characterized by schisms and in-fighting. The Chinatown preachers seem to be from the fringiest of the fringe: aside from their overt racism, they delight in practicing religious intolerance and blatant sexism. This is not true of most Black Hebrew groups; the Southern Poverty Law Center maintains a list of those they consider to be black supremacist/racist.
By DC law, people can lecture or preach in public, as long as they don’t remainin the same spot for over 30 days. I assume this is the reason the Chinatown group favors Fridays, while the Columbia Heights group is partial to Saturdays.