The home site was turned into a hub site

I am working on a new intranet and have created a home site and a hub site (both from SharePoint Look Book). The home site was not made as a hub site, but this morning, it appears to have become a hub site: in SharePoint Admin Center it is listed as a hub site and in the site settings there is a Hub Site Settings menu. I searched the audit log, and no one has been registered as having turned it into a hub site.

I this a bug or a feature?