Oy buddy... booger hook off the bang switch!!!
#1 Treat all guns as if they are always loaded.
#2 Never let the muzzle cover anything that you are not willing to destroy.
#3 Keep your finger off the trigger until your sights are on target and you have made the decision to shoot.
#4 Be sure of your target and what lies beyond it.
Also, maybe the match only allowed for certain unmodified rifles, but why would you visit for real with only a handgun? Even if you wanted to stay low profile bring a PDW in a backpack or something. Since he doesn't have to worry about ammo or SBR / suppressor laws a 300 BLK with some spare mags (along with the usual accoutrement like an optic, light, sling etc) will be enough to handle most two legged predators. Even better if he can spring for some night vision. If he is worried about mag compatibility, plenty of 9MM SMGs take Glock magazines and will allow him to hit targets up to 150, maybe 200 yards (vs 25, maybe up to 40 or 50 yards with a handgun if he is really good). He should probably change out the stock Glock sights as well, and not carry empty chamber - always have one in the pipe. Can Japanese people buy level soft / hard armor?
Also, airsoft is a lot cheaper than the real deal - and never skimp on life saving / taking gear. I hope I don't start seeing amazon special rifle accessories.