Alas
airlines should weigh and count every hand luggage. if you’re over its your problem and thats why there is never enough luggage space onboard.
Airlines that allows pax to do whatever the heck they want impose a inflight safety issue when people overstuff the overhead compartment. Not to mention the bag in question is overweight. the pax should have just flown other airlines that dont care how much luggage people bring onboard.