Does this argument commit the genteic fallacy?

While one's religion is most likely determined by familial, tribal, ethnic, and regional circumstances of one's birth it does not necessarily determine the quality of one's belief nor does it guarantee conformity with the group's ideal of a god figure. There are many examples of individuals rejecting or rebelling against their familial upbringing at an early age. 

A genetic fallacy entails rejecting a claim based on the notoriety or dubious nature of its origin.  Hitler was immoral. Hitler was a vegetarian. Therefore vegetarianism is immoral.

The term genetic fallacy does not refer to the human genome, but merely the original expression of a claim.

You're only a Christian because you were born into a Christian family. If you were born in Saudi Arabia you'd probably be a Muslim. So that should make you less confident that your God is the one true God.

There is a similar but more measured argument that atheists will use when debating Christian apologists, which is to ask if they would be a Christian if they weren't raised in Christianity. This is not meant as standalone evidence for the non-existence of God, but as a way of pointing out that a person's belief in God may be primarily informed by bias.

That said, to assert that someone would not believe in God if they had been born somewhere else in the world - technically true in some circumstances. There is almost certainly at least one place in the world that the idea of theistic religion has not reached, or at the very least isn't taken seriously. But, that isn't terribly meaningful. If you lived in a remote village where no one had ever heard of a giraffe, you probably wouldn't believe in the existence of giraffes, because that would require you to come up with the idea of giraffes existing on your own.

The second part of the statement is pretty noncommittal. Should implies some degree of uncertainty. Less confident doesn't mean that the belief isn't true, or that it's disbelieved. But, the idea that confidence depends on bias at all isn't necessarily true. A scientist who comes to a conclusion based on the strength of the evidence may have also have a bias in favor of that conclusion. Removing the bias wouldn't remove the strength of the evidence, so it shouldn't have any affect on confidence in that case.

That said, I think this walks right up to the edge of ad hominem (circumstantial) , and certainly would qualify if the speaker was more firm in their assertions.

I have to disagree with the Fallacy Master here. The genetic fallacy refers to the informational origin of the belief, not the geographical one. This statement is problematic for several reasons, however:

1) questionable cause - asserting a cause without evidence

2) alleged certainty - similar to the above, but present because of the way the statement is phrased

3) Then there is amazing familiarity 

While it is true that a significant number of believers believe in the god(s) of their culture (and in most cases, their parents'), one can never assert that this is "the only reason." This is a strong argument that shows belief in gods/religion is strongly correlated to geography but the conclusion is not clear. It is possible that one culture/geographical location got it right and all the rest are wrong. Of course, each culture/geographical location believes they are the ones that got it right... which is the really the point of the whole argument.