I’m no neuroscientist but I don’t think this has anything to do with the two hemispheres being separated - it’s just how the human mind works. When something happens we come up with an explanation for it that’s sometimes factual and sometimes completely made up. These people don’t know that they’re making it up - they genuinely believe the reason they’re giving. We’re not comfortable with uncertainty, especially when it comes to our own behavior.

I’m personally one of the people who doesn’t believe in free will so these findings make perfect sense to me and are in no way in conflict with my worldview, but I get how hearing about this might make someone else uncomfortable.