So from what I understand, meta tags "describe the content of a website precisely". Why can't two casinos use the same meta tags? Or in other way - how does the fact that two websites (with gambling content) use the same description in your opinion prove that they have one owner?
You're on the right track, but not quite there yet. Webmasters use meta tags for a wide variety of purposes.
Take a closer look at what meta tags I highlighted in the screenshot. These are not SEO meta tags but verification meta tags that are specific to each domain owner.
Here is an excerpt from Google's help page.
You can verify your ownership of a site by adding a <meta> tag to the HTML of a specified page. We'll verify that the meta tag exists in the correct location. If we can't find the tag, we'll give you information about the error we encountered. This tag is tied to a specific user. Search Console will periodically check for the presence of this tag.
https://support.google.com/webmasters/answer/9008080?hl=en#meta_tag_verificationOther services use a similar method (like Microsoft and Yandex).
There are also Paysera verification tags on the site. Paysera is a payment processor. It is impossible to use their services without verifying domain ownership first.
The verification code must be uploaded on the website only for a short time for us to verify that you are the real owner of the website.
https://support.paysera.com/index.php?/payseraeng/Knowledgebase/Article/View/519/0/1202-website-ownership-confirmationIn my free time I will try to improve my knowledge on this topic ..
You are very confident in this matter, but unfortunately I have no way of verifying this information for now.
I see that in ANN thread support answered that they have no information about it. Maybe it would be better to write directly to the tech department ..