Looks like the developer is on the bug I submitted and others experienced with export of generated scenes not working:
https://github.com/princeton-vl/infinigen/issues/330
Also Infinigen only supports usd export for the whole scene. They wrote it was because no other formats supports instancing. I discovered that GLB also has mesh instancing. I let the Infinigen team know. I hope to have an exported scene from Infinigen loaded in Babylon soon (if I can get usd to glb working with instancing or if Infinigen adds glb/glft export)