Damn. Besides looking close at the wound channel while deboning I'm not sure I look that close at the meat to see something like that. Maybe its more obvious in the flesh than the picture shows.
I found it in one of the deer I got about 15 years ago. Those little things are gross so I ended up getting rid of the entire deer. Luckily I saw it as soon as I started butchering because it was in every part of the animal.