The fallacy of argument from authority should more properly be called the fallacy of argument from inappropriate authority. Citing Einstein on God is an example of a fallacious appeal to authority. Being a genius doesn't give him special theological expertise. Citing Einstein on relativity would not be fallacious...not necessarily correct, but not fallacious. When an appropriate authority is cited, it's insufficient to dismiss their expertise out-of-hand as an appeal to authority.
I'm not anti-Christian. I'm anti-stupid.