It would naturally be against the constitution to write laws discriminating one religion.
I doubt any other religion poses security concerns. Never heard of Christian taking school full of children hostage in Russia.
Although the lawmakers might have had something else in mind too. American person became "first victim" of the new legislation. Is that a coincidence.
American man among 1st victims of Russian ban on evangelism
Donald Ossewaarde, a Baptist minister, was working in the city of Oryol, about 360 kilometres south-southwest of Moscow when he was visited by police.
They accused him of “unlawfully conducting missionary activity” by having Bible meetings at his home.
http://www.wnd.com/2016/08/american-man-among-1st-victims-of-russian-ban-on-evangelism/
Russia has a well known history of suppressing all religions and anything that could be viewed as a moral authority vs. the authority of the state.
If the intent was to go after "muzzies" then they could just choose to only enforce the law against "muzzies" and no one would stop them or criticize them
It's pretty obvious that they very much want to suppress (and persecute) Christians along with all other religions other than the state sanctioned Orthodox church
Maybe comrade Trump will bring this idea to the US as part of his plan to make us great again