Thank goodness no one was hurt. That said, it amazing how analytical people get after the ND takes place. If there ever is a doubt the gun is loaded, visually checking the chamber take seconds.
I practice dry firing a lot, almost everyday, If I have any doubt about the state of any of my weapons, I check the chamber, even If I don't have a doubt and was just handling an empty weapon, I still check the chamber. Even after squeezing the trigger on a snap cap, I still check the chamber. Doesn't matter the reason, interuption, etc, when in doubt... check the chamber, rack the slide multiple times, etc., doesn't cost a thing but time. Responses like "welcome to the club" are bull, if you follow all the safety rules, you should never have to "join the club".