His "argument" was based on numbers that even HE admitted came from nowhere.Well, that was a weak attempt at "turning his argument back on him", then and you failed miserably.
Like you said, he had an argument based on mathematical odds on the number of stars, galaxies and "yadda yadda yadda" to base his belief on.
We don't KNOW how many galaxies there are, how many galaxies have suns like ours, how many suns like ours have planets like ours, etc., so every number he was using was pulled completely out of his ass.
He had questioned the logic (and actually, the intelligence) of claiming to be science-minded folk while believing in the divinity of Christ. The gist of his argument was that HIS beliefs were logical.
MY point in countering him was that pulling unsubstantiated, unproven (and unprovable, IMNSHO) numbers and statistics to base HIS belief was no more logical than my religious belief. Just tossing numbers in there doesn't make his argument scientific if the numbers have no basis, which they don't.
He can believe all he wants in extraterrestrail life. He just has absolutely no truly logical, fact-based, scientific way to justify it. His belief that there "must" be life on other planets is just as much a matter of faith as my belief in the Resurrection, God, Heaven, Hell, etc.