I am a molecular biologist and tend to see genetic at places, where others do not. However, in this case, i find it more simple to explain observed things by memes, not genes. The same way the comparatively unrelated languages tend to borrow words from each other, if there is geographical proximity, the changeling stories and general attitude to killing babies can be borrowed and propagated.
Did you read the related links in the article?
Related: The Psychological Diversity of Mankind, An African Folktale, many of the more interesting infanticide & abortion debates on this site
A fascinating post that however might need some background reading, most relevant material is linked in the article itself. I encourage reading up on the material.
Link to article.
Stories about changelings replacing babies and the recommended course of action being basically to expose the child is not a human universal, they are found only in European cultures. These rely more heavily on guilt and less on shame to regulate behavior than most other human societies. This may not be a coincidence. The stories look like they work as a ready made rationalization to reduce guilt from infanticide. Common problems often acquire common solutions like this.