I would need some more good pics before I would venture to say anything more than what I will. Anything that is atypical often throws up red flags. The patina on the blade does not look correct for the age it is said to be, I would expect a darker more consistent patina. What concerns me most is the manner in which it appears to be assembled, the groved handle looks more like threading on a stem and the pommel looks to be at least two pieces. The metal hilt is a trait of earlier dirks, however without any provenance I would be unwilling to to part with any of my money.
All this is being said with just looking at one picture so please keep that in mind.