No it isn't, the examiner doesn't know who you are or your religion, he may not even see your name or candidate number. My English teacher back in y11 told me that the examiners basically just mark the same question over and over again done by different candidates on a computer. They have no clue who has done it and none of the teachers at your school who decide to become examiners will be allowed to mark your papers, they are banned from doing so.
To me it just sounds like a rumour some failing student (who happens to be a fasting Muslim) has decided to spread it so he/she can create some false hope for themselves because they didn't revise for their exams.