It is okay that some countries' curricula grade students on a curve. One of the benefits of grading on a curve is that students grades are assigned relative to other students' performance. This gives many students confidence, especially if dealing with a difficult subject. They may feel that they can do well in any subject. In many ways, grading on a curve levels the playing field for students.
When a country manipulates the grades of their students, other countries are well aware of it. It is an embarrassment to the offending country, and it incorrectly distorts important data. The real success of a country's education system is visible in their economy and the levels of production. Cheating is an ugly crime that helps no one.