This is merely a clip of a large group of people praying. No slight was meant against Muslims. In times of crisis, people tend to turn to God. It's clear the outbreak is in full swing, and so it makes sense that any place of prayer would be crowded. I suppose they could have shown a Billy Graham revival, but then people would be asking, "Why Evangelists??" The denomination doesn't matter, the visual of a large amount of people praying is the focus. I always looked at the scene as they chose Muslims because at the time it was not as prevalent in America and indicated that zombies were a worldwide problem. Many movies have similar visuals, like disaster movies showing shots of the Taj Mahal getting leveled. It's not meant to indicate hostility towards India, just that the disaster was global and they used instantly recognizable landmarks to convey that.