Wow, you’re right. When I first read that sentence I assumed that he meant that the gun went off when he fell down, and it fired into his arm - into his old wound from the war - and that’s why he worried the new bullet might have dislodged the old one, along the lines of https://pmc.ncbi.nlm.nih.gov/articles/PMC3846953/ or https://pmc.ncbi.nlm.nih.gov/articles/PMC5731308/
But then I reread it and it says,
Sheehy himself has sought to parry Peach’s version of events by saying he had never been hit by gunfire that day in 2015.
So you’re right. The bullet would have to be dislodged by his act of falling down. I’m not a medical or a firearms expert so I can’t say for sure on this point, I can only note that my internet searches don’t seem to come up with any other examples of this ever happening.
I guess Sheehy might have gotten irrationally worried over nothing that day - a strong enough fall can do that and much worse to the good ol’ noggin, I suppose. But that also means he never tried to get a bullet removed after so many years? Isn’t that really dangerous to leave the bullet in? And couldn’t the doctors who saw in in 2015 tell if the bullet was recent or really old?
Also, he has confessed to telling the ranger back then that he shot himself. Surely the ranger would have known he was lying or not if he saw the wound? You’re right again - it doesn’t add up.