Webtunnel documentation clarification

https://community.torproject.org/relay/setup/webtunnel/source/

This part, and more specifically the "by default" part in the Webtunnel installation documentation is a bit confusing, at least for me.

Does the attached paragraph means webtunnel bridges can only be distributed through HTTPS or it means that if no mechanism is defined in the torrc it'll use the HTTPS distribution mechanism?