Not that I can't think of possibilities, but I won't even offer them because at this point it's anybody's guess and anyone's opinion could be debated or questioned by someone with a different opinion of equal or lesser validity. Short of a veterinary professional or lab examining the fish it's guesswork anyway at this point. I would take it as a good sign, not obsess over it, and not worry about whether the hole will close back up because it's possible but not to be expected and not critical to his future health.
As I mentioned earlier, from the science literature I've read on it, there are brief and specific windows for the preliminary biochemical steps leading to healing that have to take place. They've likely either happened by now or they haven't. What I've seen over the years as a mod on other forums tells me the holes sometimes heal under the right conditions, but more often not.
Bottom line is it's good to hear he has apparently recovered and let's hope that's that. I've had a number of green terrors, a favorite fish of mine, and none were prone to health issues, so given reasonable care I wouldn't be surprised if he goes on to live a healthy life.