Sado is known as "뜨용 (Tteuyong)" in Korea. He did boosting to earn money as part of the boosting team named after his BNID.
I guess you need to understand the background of this story. He was once a member of an amateur team and the team participated in a local tournament which gave winners a chance to compete in APEX. During the online preliminary round, he didn't appear in the match just because he overslept (based on his excuse). However, the team managed to win the online match with a substitute member and advanced to the offline tournament. He once again did not appear in the offline match just because he didn't want to travel from his hometown to Seoul, the tournament venue, saying that he lost his interest in playing Overwatch. And what is worse was that he informed the team of this after the period for player substitution and therefore his team couldn't have time to find a substitute player, leading to disqualification in the tournament. And the team disbanded. The team leader left a post on Inven about this to let other teams know about his negligence and found out that Sado did similar things not only in his team but also in other teams.
This made Sado blacklisted among Korean Overwatch teams and therefore he couldn't find any team to play with. That might be a reason for him to start boosting for illegal money.
For your information, people here in Korea hate boosting more than trolling in the game. Might be second to hacks.