Well, my own personal viewpoint on whether or not this should be considered a keris should carry little weight in the community at large, but i see this much more as a keris than i do a jambiyo. I mean, everything else that one would expect from a keris is there except for the curvature of the blade. At the same time, certainly the curvature alone cannot qualify a blade as a jambiyo any more than a wavy luk blade can qualify a blade as a keris without the other recognized elements that make up a keris.
The blade looks genuinely old and the curve looks intentional and original to me. Certainly this is out of pakem, and i do realize that for some any keris dhapur that is outside of pakem is not a true keris. But i would happily accept this particular example into my family of keris and would consider it one, albeit a strange bird in the flock.