What is "Peripheral Dogma"?
I think the author was just trying to make a point that while the "central dogma" is indeed key, there is more to it than that and that understanding of molecular biology has advanced beyond being simplified to that one tenet. Without having the passage in front of me, the ideas you gleaned from the paragraph make sense, though others such as epigenetics seem like they would fit as well.

As you've noticed, this term is difficult to find anywhere else, it isn't a standard term and therefore doesn't really have any meaning unless it is defined in the source. I wouldn't recommend using it yourself unless you plan to define it. The Wikipedia page for central dogma that you linked has a whole section on information transfer not included in the "central dogma" - I think you can safely assume the author was referring broadly to these items.

This all may be a bit of a joke, as well, given the definition of "dogma" and it's somewhat inappropriate use in the context of the central dogma of molecular biology - again, the Wikipedia article you linked talks about the problematic use of the word "dogma" in this scientific context.