Hello Detlef and thank you for adding your thoughts on this unusual knife. The name "Eyaya" comes from "Resource Management In Ancestral Lands The Bugkalots In Northeastern Luzon" By Dante M. Aquino. This was sent to me by our good friend Lorenz. There is another name also mentioned in this paper, one that I should have mentioned when I first posted this example. That name is "Kumpat" meaning curved scythe for harvesting rice. After reading the responses from everyone I now believe that Kumpat might be a more appropriate name for this knife. I wish that some day I could find an example such as the one you have in your link to go with mine.
Best,
Robert