The phrase "coincidentally about" is correct and usable in written English.
It is used to describe something that happens by chance or by coincidence, but is related to the topic being discussed. Example: "I was reading a book about dolphins when, coincidentally, a documentary about whales came on TV."
These diaries are coincidentally about creatures that like to tunnel, but otherwise take sharply contrasting approaches.
It has the lowest rate of obesity in the nation, and not coincidentally, about the lowest rate of diabetes.
Instead she resigned via Twitter just after 9am on Tuesday, coincidentally about three hours after a three-day ceasefire had come into force.
She stars in two movies opening today: Jean-Pierre Jeunet's "Amélie" and Laurent Firode's "Happenstance," both of which are, coincidentally, about coincidence.
In 2004, the top Emmy winners were "Arrested Development" and "The Sopranos"—two brilliant series that were, coincidentally, about rich criminal families.
Coincidentally, about the same time, the NBC employee who had originally opened the Trenton letter remembered that she had put it aside and decided to alert NBC security.
This is far from the first time that models have been singled out, and not coincidentally moralized about, as potentially unhealthy and somehow inherently bad.
The hotel burned to the ground three years after it opened--coincidentally, about the same time business had taken a turn for the worse--but the cottages remained.
President Carter, who was ostensibly honored in 2002 for his work with the Carter Center spoke in Oslo, not coincidentally, more about the evils of war than he did about the Carter Center.
Ms. McPhee, coincidentally, is about to star in NBC's "Smash," which is being slotted on the schedule right after "The Voice" on Monday nights.
He earned a place among journalism's shamed stars by playing it fast and loose in a story, coincidentally enough, about a cultural icon known for liking his facts slippery.
