Thanks for the correction. It's been many years since chemistry class. However, this information does not support my current beliefs and is inconvenient to my purposes, so I'll be writing my congressman to have those pesky ideal gas laws repealed. :-)
Oxidation is sherry, paper or wet cardboard-like. Fortunately, carbon dioxide is heavier than oxygen, so, unless the carboy was exposed to drafts, the CO2 in your secondary settled to the bottom and kept out the O2. It's probably fine!