There's no evidence shown in that article that anyone was racist so what are the FA meant to do? They can only deal with facts and evidence.
Likewise this, if there's no evidence what do you expect to happen? The team were losing and the only people that heard it were all on the bench for the losing team? Come on. I'm damn sure that if anyone heard it on the opposition bench they too would have made a stand as there's no place for racism in society. But on the facts given in the article, what do you propose happens? Let teams walk off the pitch when they're losing citing racism and then oh ok it might have happened it might not have but we'll replay the game/award you the game.
Football is hardly the most sportsmanship sport at the best of time any opportunity to gain an advantage would immediately be abused if The FA set a precedent of making decisions without evidence to support them.