Have you worked with either before? They’re completely unrelated technologies, with similar names. They have nothing to do with one another. They’re not even being developed by the same groups. They emphatically do not have the same fundamental premise. I’ve built apps in WebRTC before, and I can guarantee it has nothing to do with WebUSB, and in fact I just confirmed in the docs that it has nothing to do with any sort of device-level hardware control.
To reiterate: the only connection between WebUSB and WebRTC is the fact that they’re named “Web” + three letter initialism.