It's part of Korean culture for someone's "superior" or "teacher" to use "physical discipline" on their subordinates or students. It's actually part of many traditional cultures, just less often practiced in developed countries. And of course, it can manifest in different ways, from slaps, getting hit with objects, getting things thrown at them or worse. It can occur every once in a while or be part of unspoken company policy. It can be adults hitting adults, or adults hitting children. The person doing the assault may think they are doing the right thing or they may be fully cognizant they are bullies abusing their power.
Next time you see bruises, don't assume it's "just from practice".