The more I research, the more I'm inclined to believe you are correct. The check engine light most likely had nothing to do with the octane and was just coincidence. I guess if the code comes back after a full tank of premium, I'll know for sure.
It's a 2009 with about 46,000 miles. It's actually a 3.0 liter. I have no idea why it's a 228 and not a 330.
Although I think my wife was somewhat crazy to get rid of her newer lower miles car, I must admit that I love driving her car. It has all-wheel-drive and a manual transmission for extra fun!