Based on the URL, it appears that those are taxonomy term results from the pa_isbn taxonomy.
I suppose you want to search ISBN, but not to return as results. On the General Options -> Sources 2 panel under the Return taxonomy terms as results make sure that nothing is selected: https://i.imgur.com/ZEIa2VB.png
That option is to use if you want to return those taxonomy terms as results. You already have the Search in terms? option enabled, so these fields are searched as well when looking for products.Best,
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