"The garand bolt isn't a mousetrap waiting to snap on the first thing that brushes against it. A properly locked-open garand bolt will only release when a loaded clip is inserted, bottomed out, and released, OR the follower is depressed significantly. Many require the follower to be depressed AND the op rod moved to the rear to release the catch."
Another correct response. Garand thumb useally happens while you are watching the last few minutes of Saving Pvt Ryan after about 8 beers when playing with your Garand.
I have seen 6 or 7 garand thumbs during the high power service rifle matches in the winter time. I havent seen any during the warm summer high power matches. All of these came from experienced shooters, but they all had different explanations for it,(excuses). It does happen. You are right that it shouldn't happen, but it does happen. I have also seen it happen with one M14 and one M1A, during a high power rifle match in the winter time. I dont remember thier excuse, but those both happened on the same day. NONE OF THOSE happened while some old dude was drinking beer sitting on the couch watching old war movies. These were all in the field incedents. The guy with the M14, and the guy with the M1A were single round feeding during the slow fire prone at 600 yards. Nothing gets everybody's attention on the firing line like a guy rolling around with his thumb stuck in the action of those rifles. Except a real accident, like the AR-15 I saw explode from a compressed round, or out of battery epic fail. At least thats what they called it after they found the pieces. That guy got minor injuries, but thank god it didn't happen on the Airforce Base Range, or the Army Range we often use. They don't mind the garand thumb, but you screw up thier spotless accident record on that range and your whole team gets the boot. At least that's what they tell us anyway, I believe them.
ALSO: you shouldn't ever be drinking alchohol, playing around with your weapon anyway & if you do, you need a refresher course in proper instruction on firearm safety, or new head gear, take your pick.