1) Monozygotic adult twins have similar religiosity.
2) Dizygotic adult twins lack similar religiosity.
How would you explain this finding?
Twin studies are notoriously flawed.
Anything like this which argues that a nuanced behavior like religion is "genetic" is suspect.
Your questions are FAR to simplified to be reasonable when it comes to human genetics. It is like the gene studies which argue alcholism is inherited without considering the issue more of pain/pleasure reception not a Jack Daniels/Johnny Walker/beer issue.
This study might as well say that monozygotic twins tend to dress the same and fraternal twins do not have that tendency.
as I said, garbage in garbage out.