A glock isn’t going to go off unless you pull the trigger and teh last time I checked a bowling ball doesn’t have fingers.
I’d guess a cheap gun of the variety that fires when you drop it.
if something is through the trigger guard where is can be pushed against the trigger then the Glock is an accident waiting to happen. Never put one in your pocket with the trigger uncased.
Gives me the heebie-jeebies when I read about ADs when holstering the Glock where the trigger finger is not sufficiently retracted. These almost qualify as actually accidental.