Not that it makes me happy, but the explanation is helpful!
But the strange part is that I can’t find the information from the custom tab on google at all, not even with site:planetayurveda.nl in the query. It is non-existent. And the other strange part is that the info from the default Woocommerce product tabs does show up in Google.
Maybe Google et al index it for ranking purposes, but never to show it up anywhere in a search query.
Now because of that, I am in the progress of re-writng all my product information to have all info available on google and thus also on the main page of the product. When done it will actually make the custom tab obsolete, with which I am not happy, since the tabs make the information more organized for which I started using it in the first place.