You wouldn't expect the actual disk I/O to be different. The VM has overheads in transporting the data; that's what the article is trying to measure.
And with that in mind, the "native" bars are pretty much useless in this article. They should always be higher than the VM bars, unless specifically trying to test fsync - and since it seems fsyncs are ignored, the test isn't being achieved.
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You wouldn't expect the actual disk I/O to be different. The VM has overheads in transporting the data; that's what the article is trying to measure.
And with that in mind, the "native" bars are pretty much useless in this article. They should always be higher than the VM bars, unless specifically trying to test fsync - and since it seems fsyncs are ignored, the test isn't being achieved.