Even if you are a foreigner, in addition to government regulations, you also need to comply with the regulations of the bank/company where you work. You are their employee and you need to follow their rules, and with the anti-gambling culture in Korea, it is no surprise that banks would prohibit gambling.
Whether he used the bank's computer or his phone to gamble, it was the same, since he gambled during working hours, his superiors had the right to handle it according to company regulations.
Stealing money from a bank/company is never easy but for a gambling addict with no money to gamble anything is possible.
That is totally not banks business what I am doing with in my phone. That is a violation of privacy. How would they even find out that I am gambling on my phone? By looking on the screen? If that is ok, then it would be ok to browse my chats and phone call list? Absolutely not. An employee is not a slave that has no right to spend a minute to take a rest. Then everyone should immediately get fired as soon as they went to a toilet to get a cup of water.
For addicted anything is possible, but from my experience, to steal from bank, where cash is monitored by dozens of cameras, and UI wont allow to make a transaction to a random account without receiving a permission, is close to impossible. Imo the maximum what addicted can steal is money from his colleagues.
The thing is, banks hire and pay you to work for them, they don't hire and pay you to gamble at work and during work hours. If you want to gamble or do anything on your phone, do it at home during your break or anywhere else, not at work and during work hours.
If you were a boss, would you be happy to spend money to hire employees but they do not work hard and only spend time gambling during working hours?
Don't compare going to the toilet, drinking water... with gambling during work hours, that's pretty lame.
Whether it is customer money or co-workers money, it is theft and is taboo in the company. That is why every company has its own rules and regulations that employees need to follow, we need to take preventive measures instead of letting things happen and then trying to solve them.
If I was a boss, my duty will be to provide him with work non-stop, and pay accordingly. If employee has done all his work, works 9 to 5 and there is still time till 5, but at the moment has nothing to do (or he waits for others to give him work), I would not mind if he would gamble at work. And comparing toilet and drinking water with gambling isnt lame (As an example, I can go to a toilet and gamble 5-10 minutes there). This all means being at work during working hours and not working, same as reading new, scrolling social media. If it does not interfere work result, why should it be not allowed? Most important, employees get paid hourly, or had a contract. Employer does not stand behind them with stopwatch and pay only when employee is really working.
People are different. One and the same job at bank different employees can do differently. One can do it in 30 minutes, other will struggle for 2 hours. But at the end they will get paid equally. This is not a race, where first to finish gets paid more. If job is 9 to 5, and employee has done all his work, the rest of his working time (in case new work appears) I would let him do whatever he wants that is morally acceptable and dont violate any rules.