So, although I can't find the study itself, it seems that the antioxidants in blueberries have an affinity for protein. This post gives a little detail.
"This study suggests that the best way to gain maximum benefits from blueberries and other fruits eaten for their polyphenol content is to consume them either one hour before protein is consumed, or two hours after."
The thing you don't know is whether that is a good thing or not. Perhaps the antioxidants in blueberries are helping digest the protein or performing a beneficial task. The study was only looking at the antioxidants in the blood stream. And also, the study suggests protein but is that animal protein only? Or all types. They only tested with milk for some reason.