I don't think that a bullet wound. His spine would've too badly damaged from a bullet. I'll say that's a wound from another deer or a limb that got infected
Actually, I'll bet it is... I shot at a buck about 300yds on a powerline the weekend after New Years. All we ever found was a huge pile of brown hair. Honestly, the deer didn't react all that badly, just took off running like he was on fire. Last Saturday a boy killed that deer in almost the same spot crossing that powerline, the wound looks literally IDENTICAL to that, seriously the same size and depth wound. I don't know how the shock didn't at least momentarily stun/paralyze his spine.