This, pretty much.
Most people have a higher threshold than sportsmen. If you're just a regular person with a regular job, you only have a "drinking problem" if it causes you to miss work, or if a student, miss classes/get bad grades because you were drinking the night before an exam or drinking instead of doing homework, etc. I don't know about you, but I imagine most jobs, you can show up to having drunk quite a bit the night before, and while you might be a bit hung over, you'll still be able to do your job for the most part. I've learned the hard way that while I can get trashed on a school night and be fine in class the next day, if I pulled that stunt before I had a training session or match for whatever sport I was involved in at the time, the results would be pretty horrible.
Not to mention, being a professional, it's his job to stay in peak physical condition. I can't imagine you can get away with much drinking to stay that fit. In contrast, maybe the amount he drinks is relatively moderate compared to someone who's not a professional sportsman but they don't have a job that demands they stay super fit year-round.