Censys gets these defaults (you could probably measure a slight bias in their data towards alphabetically earlier names as a result, but I have never checked) for sites using Apache, and for other servers with a default they get that default (in nginx I believe you have to explicitly configure a default if you want one). If there is no default the site says you need to specify which name you wanted or too bad.

You'll see the same for various other providers that crawl the IPv4 Internet looking for services. My last job (it seems prescient now to have no job, very convenient in current situation to have no reason to go outside anyway) had me trying to fit some of this data to other service discovery information.