Where have you read that? Until mid-2014 I lived a few mins drive from Moss Side, and drove through it on my way to work. I lived in South Manchester from 2010 until then, and moved to Stockport/South Manchester border early last year.
There's no way Moss Side is mainly Muslim. It's such a melting pot. There are a couple of spots that are pretty Muslim heavy, but there are also spots that are Afro-Caribbean and others that are white. The place is absolutely massive. It's got roughly the same population as the Vale, but seems bigger and more spread out.
Sounds to me like whatever you read was sensationalist bollocks, but my evidence is anecdotal so I'm open to being wrong.