Underlying assumption is that his opinion on the matter counts, i.e. it's an "appeal to authority". Unfortunately, there is no direct authority on the existence of God, but only those who are experts on the "creation" (eg biologists, cosmologists, physicists, archaeologists, sociologists, anthropologists, etc).
Einstein (and note the correct spelling, Kate) was a deist in general, but he was most definitely an atheist for Jehovah, the Abrahamic God of the Bible, and repeatedly made that point clear when he said the "God" he was discussing wasn't the one you want him to be, eg the being who wanted to have a personal relationship with his creations, wasn't interested in human affairs, didn't send his son Jesus to die for your sins, didn't create the Earth as depicted in the Genesis account, etc.
And just as long as he wasn't an atheist and didn't speak up too loudly about his deistic beliefs, he was OK and people didn't hate him for his beliefs in God. He was obviously smart enough to know that believers and non-believers alike would interpret it to mean what they WANT him to mean.
Yes, he was raised in a secular Jewish household, but the German State forced all families to teach their children some religion in the home via mandatory rules (to supplement secular education in the public schools). Around 12, he discarded beliefs in the accounts found in the Torah, and wasn't a practicing Jew (i.e. he didn't observe the Sabbath, keep kosher, etc).
Imagine that: Einstein, a genius, was smart enough not to get dragged into religious arguments! (And when he spoke of 'religion', he didn't mean what you thought he meant, but was speaking more to the sense of mystery, where his religion WAS, for all purposes, science. He makes that point clear in his autobiographical book, "The World As I See It", written in 1956).
Another book on the subject is "Einstein's God", written by Krista Tippett and featuring interviews with his friends in the world of science, analysis of his writings, famous physicists, etc.Adam