It is about McDonald's, as a corporation, refusing to remain neutral in the culture wars. McDonald's has chosen not to remain neutral but to give the full weight of their corporation to promoting the homosexual agenda, including homosexual marriage.
As if you had any doubt of the AFA's homophobic agenda, Think Progress lists some of their other less than successful boycott attempts.
AFA has a long history of silly, offensive boycotts against, among others, Wal-Mart (for selling “Brokeback Mountain” DVDs), Ford Motor Company (for advertising in gay-friendly publications), and the American Girl dolls (because the maker contributed to a youth organization that was pro-choice and supported the acceptance of lesbians). In 2005, it called off its unsuccessful nine-year boycott of Disney (for its “embrace of the homosexual lifestyle“).
Like Disney that saw record profits during the AFA's 9 year boycott, I doubt that Mickey D's is shaking in there boots right now, even if they are blue suede and match their outfits.