That’s I believe woefully inadequate. There are some levels of code similarity:

Level 0: the code is just copied

Level 1: the code only has white space altered so the AST is the same

Level 2: the code has minor refactoring such as changing variables names and function names (in a compiled language the object code would be highly similar; and this can easily be detected by tools like https://github.com/jplag/JPlag)

Level 3: the code has had significant refactoring such as moving functionality around, manually extracting code to new functions and manually inlining functions

Level 4: the code does the same conceptual steps as the old code but with different internal architecture

At least in the United States you have to reach Level 4 because only concepts are not copyrightable. And I believe chardet has indeed reached level 4 in this rewrite.