Let's suppose for a second that the numbers are biased in the Java databases' favor. I doubt that other benchmarks would show such dramatically different results that would have those databases losing by much. So maybe they're not ahead as those number show (though I have little reason to doubt them), but a little behind. The difference would still not justify the claim that C++ provides superior performance for databases.

Also, it's an open source database with no commercial support by the authors, so I wouldn't really call them "vendors".