It looks like a mistake, but it isn't. The question translates as 'Who is it who's right?'. It just looks odd because the informal French word order means that the two 'who's' are next to each other. The first 'qui' the question word 'C'est qui..?' and the second one is the relative pronoun.

But in french it is a fault to use this sentence , noramlly you say "qui est ce qui "

Many people say it (I do), but it's much frowned upon. A more correct way is simple "Qui a raison ?"