Thats my fear as well, i use elevator like 4 to 6 times a day with my dog. What if one time I don't pay enough attention, or the dog hears sth and suddenly bolts. Not that long ago puppy died in my country cause she bolted out of elevator door, the owner wasn't fast enough. The elevator company had guts to even bill the poor owner who already had to move out from her aparment cause of ptsd she got over the incident.
I feel like that owner rly needs to change the flex. Flex has such thin line that no elevator can caugh it (some elevators stop if they detect that sth is between the door if it's thick enough, but how thick it needs to be depends on elevator). The dog can go rly far away with flex and you don't feel the dog similar way from other side the flex as you would with leash.
Thank god for that man. The dog would been goners.