Yes, it is that minang flavor that had me thinking Sumatra.
Now when it comes to "authentic" i think we need to define our terms. I would like to think that in some respects the keris arts are still active and evolving. If this sheath were to be presented as an old and classic form we might be right to question it's "authenticity". However, if it is recognized as a new sheath form i would have to say that it seems a beautiful and well executed expression of contemporary keris arts and in that it would be quite "authentic".
The blade, of course, is another matter...