Three kinds of candidate
A host candidate can carry a private address such as 192.168.x. A server-reflexive candidate is the address a STUN server observed. A relay candidate is a forwarding address.
Candidates are listed on the WebRTC test. Candidate lines are not uploaded. The same page explains host, server-reflexive, peer-reflexive, and relay candidates, the Scan browser button, and the 4-second gather.
Why .local is not a leak of the LAN IP
Current browsers often replace the raw host address with a name ending in .local. The page cannot turn that name back into 192.168.x.
Treat .local as masking, not as the private address itself.
What this does not prove
No candidates usually means WebRTC is blocked or unavailable, not that a hidden IP was invented for you.
This page does not guess DNS resolvers. A VPN may or may not change WebRTC; the brand name is not the result. See what a VPN leaves in place.