Heh no worries, there’s a little mismatch between Rhino’s concept of PBR and ours — the Bella materials that correspond most closely to Rhino’s Physically-Based Material are the Uber & Principled types, where you get control over a whole bunch of parameters (Uber gives most control, Principled exposes just the most-commonly used).
Then, you have our PBR material, which just accepts a single path — it can be one file in a matching texture set, or it can be a .zip file containing a texture set. In the former case, there is logic inside that scans to find the other the textures in the set, using the supplied path as a prototype. These types of PBR texture sets are intended to encode all the necessary information directly in the textures, so the PBR exposes very few parameters.
Rhino’s Physically-Based Material also has a function you can use to set it up based on a set of textures, and at some point the Bella Uber & Principled materials will gain a similar function, though I consider it generally preferable to just use the Bella PBR material.
I’ll mention that there is one thing with PBR that can potentially trip you up, and that is that I cannot yet support Arroway texture sets, because they use a peculiar naming convention for the textures. I am working on that, but in the meantime, if you wanted to use an Arroway set, it would be necessary to rename the textures to use the more standard file_color.jpg, file_normal.jpg, file_roughness.jpg (and so forth) naming.