It's typically used in sports and means an athlete or team has won championships in an international league, or a person is an Olympic athlete.
Coding is less explicitly competitive, but there is an element of competition to it. If you were a major contributor to a project that had displaced multiple international competitors, that'd clearly be world class. For example, Linus is a "world-class" coder because Linux is used all over the world and has displaced many operating systems.
That you are good enough that people would accept your work in the United States?