Don't fret too much. He may have had EHD and survived. Or it could have been an injury, or one of a zillion other things that affect deer. The first two pics below are of a deer in 2020 that looked emaciated like that. For a 4yr old deer, he probably didn't weigh 100lbs. I named him Splinter because he looked old & broken & frail like the rat on Ninja Turtles, and he had a splintered brow tine. You could see his ribs, hips, even his vertebrae. I didn't think he would make it through the winter. But the third & fourth pic show what he turned into a year later. Same deer.
I know it looks like they're in misery when they're all skin & bones like that, and they probably are. But don't underestimate their ability to survive and come back STRONG. The good Lord designed them to be resilient.