I looked into the case, and as far as I can tell he never spawned a minigun. My guess is that he used, as Mia said, a hack that allows you to shoot from inside the vehicle (mostly used as some sort of driver-db, in which the driver can drive-by with some weapons). So I think he never actually spawned a minigun, but was using this kind of hack to shoot minigun bullets, and that is why the AC never picked up on it.
Now, I haven't had a lot of time lately to improve the AC, but I just did an update which makes the weapon AC autoban. There shouldn't be any bugs left in it now. I'm not going to use a script like Tree suggested, because it's very rigid and doesn't allow to give weapons. I wanted a more dynamic weapon AC, so I wouldn't have to change it if I ever decide to allow other weapons, or when admins give a player some weapon. Also, a lot of problems with the weapon AC were caused by GetPlayerWeaponData returning false data (it would return the old weapons when you were still spawning or just spawned, ...) and due to players being desynced and ending up in a class with the wrong weapons. But, all of those problems should be fixed now and it should work fine (hopefully).
Fixing all of the AC will take a lot of time though. I can only make small changes at a time, then leave the script running for a couple of days to collect data, then go through all of the AC reports generated during that time window, checking every single report if it was a bug or if the player actually hacked, then fix the bugs (or add debugs) and repeat the process. So it's a very time-consuming task, and it will probably take a lot of time to fix completely.
About adding new admins, we added 2 mods who aren't admin yet, so let's see if that makes a difference first. We'll review the situation after that, then decide if we need more or not.