I checked too and found nothing identical (although certain body parts are very similar to a few RO sprites), which is why I decided to post telling them to mention that they're going for the RO style instead of doing something drastic but unfounded. They did such a good job that it could easily be confused for a frankensprite with a few modifications because of the similar body parts and colours. Plus, it's just common etiquette, and I think that's worth informing people of :]
I think the only assumption that can be made is that this user doesn't write a lot (and maybe doesn't even understand english language). I tryed to search some ragnarok sprites and I didn't found something equal.
I think that everyone should be considered not guilty until proof of guilt are found and I found nothing else than that he used a very similar style. (maybe too much similar)
... surely the eyes are different from Ragnarok standard as you can see there. 
That's what I think... 
You may want to mention that this is meant to be in Ragnarok Online's style (and if you referenced any sprites while working on this in any way, mention that too). Pixel art is a small world, and theft is common enough that if credit isn't given, the common assumption is that you're trying to hide your sources.
I perfectly understand. You made a good work informing about the etiquette.
(and I really appreciate that you made some search too
)