Does that really matter. He's using Python, if the function is part of the standard library and if it's implement in Python or C doesn't really matter.
You can look at it that way, but still, the fact that most of the work in the Python version is done by C code makes the timings less surprising. If split() was implemented in pure python and it would be only three times slower (when run with CPython) than std.algorithm.splitter, that would be very surprising and a sign that std.algorithm.splitter is doing something horribly wrong.
