You get the impression from the article that the normal white-populated agencies did these McDonald’s ads. Wrong.
In 1971, Tom Burrell started his own ad agency in Chicago called Burrell Communications. Tom was an African-American guy who began a trend with agencies specializing in creating advertising targeted at African Americans. He began with accounts like Coca-Cola, Philip Morris, and McDonald’s. So it’s very likely the ads you showed were done by Burrell or another African-American agency.