I'm with you here, but I see another problem.

The expected functionality of chardet (detect the unicode encoding) is kind of fixed - apart from edge cases and new additions to unicode, you'd expect the original and new implementations to largely pass the same tests, and have a lot of similar code such as for "does this start with a BOM".

The fact that the JPlag shows such a low %overlap for an implementation of "the same interface" is convincing evidence for me that it's not just plagiarised.