He didn't get bit.. I mean the bite didn't pierce his skin, the blood on his shoulder was from the zombie's teeth getting destroyed after biting the vest
i dont think thats a plot hole and will eventually become something important to the story because he himself says it "didn't feel like being bitten i should know" so its probably not a plot hole
Plot hole: he got bit but didn’t turn into a zombie?
Also, since he got bit, he just have a wound… did the doctor not see it? What?