As the extension’s description says, you have to open the publisher site (e.g., O`Reilly, IEEE, Elsevier, and many more - these examples are typical in the field of Computer Science) or another website containing bibliographic information. For the latter, they give the example of “arxiv”. Therefore, I assume that pages containing search results (i.e., Google Scholar) do not include the bibliography directly or in any way readable for the plugin.
If you follow your link to the Google Scholar search result, you will get to a literature page. Unfortunately, even this page seems not readable by the JabRef extension. But you will find a link to arxiv at the bottom of the page. If you try to add your targeted paper from its arxiv page, it’s working fine - I tested it to be sure.
To conclude this thread, it seems like there is either an issue or a feature request.
If I correctly assume that Google Scholar is not supported by the JabRef extension, there is a feature request to support Google Scholar as a source.
If my assumption is wrong, this is a bug report that the extension is not able to read bibliography from Google Scholar search results.
Maybe @Siedlerchr could help us out here. Nevertheless, the extension is working but you may need to adapt your workflow to the tool as I described above. Check out the literature and switch to the individual paper’s page (i.e., publishers site, arxiv, other search engines which provide detail pages for papers, e.g., semantic scholar). I assume, that this is the easiest workaround for your issue.
If you do not rely on using the extension for Chrome, but want to use online search engines (e.g., Google Scholar) as a source, I recommend to read Searching externally using Online Services. The manual describes how to open the dialog of that feature and how to search for literature. It also describes how to create complex search terms. Unfortunately, Google Scholar is not supported at the moment since Google changed their API. However, you will find a list of all other supported databases there.
I hope that I could help you with your issue. Feel free to reply or ask further questions.