Given they've literally just deployed a copy of an open-source website, I'd guess it was a mistake rather than malicious: possibly someone who was testing out vultr's hosting or perhaps someone trying out docosaurus (given your website is listed in their showcase as open-source: https://docusaurus.io/showcase). Easy enough to imagine someone running through a deployment process that intelligently recommends a domain to register for them.

If malicious, it's probably not about the site content and rather they're sending out emails pretending to be you.