Howdy!
I couldn’t find a technical issue with your site that is causing this behavior; this issue is only with how Google chooses to display your website.
The meta description for that page is “Fast alle Menschen werden bewusst oder unbewusst vom Belohnungssystem im Gehirn motiviert.”
It doesn’t contain any of the words you used in Google Search to find your page. So, Google took a part of your content and displayed that instead.
From Google’s documentation about snippets: https://developers.google.com/search/docs/appearance/snippet
Snippets are automatically created from page content. Snippets are designed to emphasize and preview the page content that best relates to a user’s specific search. This means that Google Search might show different snippets for different searches.
Snippets are primarily created from the page content itself. However, Google sometimes uses the meta description HTML element if it might give users a more accurate description of the page than content taken directly from the page.
The same goes for the title — Google ignored it and showed what was related to the search query. If you want to learn more about that, see https://developers.google.com/search/docs/appearance/title-link.
To make Google more likely to display your preferred meta titles and descriptions, you could try adding more “keywords” to them. We have a tool to help you with that: https://tsf.fyi/e/focus.
However, people don’t always search for your keyword but an inflection or synonym thereof. And because Google only knows the English dictionary well and not German, using focus keywords is not guaranteed to help. For example, they don’t consider “Menschen” to be an inflection of “Mensch.” So, if someone were to search for “Mensch,” Google would still not match that with “Menschen” in your description. While if you search in English for “Person,” Google will also show results about “Persons,” “People,” “Human,” “Humans,” and “Beings.”
I hope this clears things up. Have a lovely day!