I agree. The headaxe of Northern Luzon is an endemic development.
The tribes of Northeast India and Northern Luzon have remarkably similar ecologies and material culture. On the other hand, the social organizations are very different. Also, I also doubt that the headaxe of Northern Luzon and the axe of Northeastern India had come from a common origin, because there is yet no indicative proof. This is not to say, however that both cultures had not adapted certain cultural traits from a common influence or source (directly or indirectly). Talismanic symbol in blades of India is also found in some blades of Northern Luzon (Ilongot and Agta), and Southern Philippines (so called "moro" blades).
Meanwhile, here is a photo of a headaxe with a centipede design – in relation to the thread:
http://www.vikingsword.com/vb/showthread.php?t=6818