In an open circuit, are capacitors still in "series"
So, essentially, what I'm asking is when can we assume two capacitors are in series and why are they not in series in the image below?


They are in series.

Only your conclusion that they have the same charge now that they are in series is wrong. Why would they? They've got charged somewhere else, and since the charge on the rightmost plate of the capacitor can't go anywhere, things stay like they were.