No worries, I've moved your post to its present location.
Well, the paper/substrate doesn't really mind what kind of emulsion is applied to it, so there's no technical reason why a paper base would have to use a non-panchromatic emulsion. There's a practical reason why in a home setup it's more challenging to work with a panchromatic emulsion: part of the work needs to be done in the dark, including the coating/application and drying steps. In an automated process as is likely used for the manufacture of Washi products, this is less of a concern since it can simply be done within a dark space.
As to the emulsion - I don't know what they use, specifically, but also here there's no major technical challenge involved as it's fairly straightforward to make a simple, panchromatic emulsion. This is even true in a home darkroom, although as said part of the process needs to be done in the dark. IR night vision goggles can be used in this case.