No, it doesn't really make sense from a Christian point of view. It would make sense to believe that muslims were following the wrong path to God, or misguided, or something like that, but saying that muslims are worshipping Satan is only sensible for Christians of the Westboro Baptist type. Joining the BNP would be consistent with that type of Christian fundamentalism too - hatred of gays, Catholics, muslims, Jews, Hindus, etc.
It does make sense once you look at the concept of false prophets and the Book of Revelations. The Anti-Christ will be a false prophet which represents the Beast but is seen as a representative of god by the many of the masses. False prophets if not cons are guided by a spirit which is not from god. In this case this spirit would be of the Beast, representative or lower demon or the Beast directly. This also crosses over for Christians being on guard against spirits which would led one astray. these spirits would be of part of the Beast, a representative or the Beast itself.
Most Christians are PR friendly They will not outright tell someone they are going to burn in hell, face oblivion or follow a false prophet. However by their very belief that one must accept Christ as the Son they already believe it. Since Mo claimed to hear his message from an angel a Christian can be justified in claiming either Mo had mental issues, was a liar or was led astray by a false spirit. If they take the claims of this angel middle-man as fact then in the Christian mindset a Muslim does follow Satan but does not realize this fact. It takes no leap to make this conclusion.