Thanks for following up with us, @julia77. We are afraid to say that we don’t have a specific option to exclude certain database columns from the link indexation unless you do it programatically.
If you’re familiar with WordPress plugin customisation, you could go ahead and exclude the relevant columns from the link indexation as well.
That said, as much as we hate to say it, your question goes beyond the technical expertise of me and my colleagues on the Yoast support team. This means we can’t give you a solid answer to your question.
But we don’t want to leave you empty-handed either, that’s why we’ve created our developer portal at developer.yoast.com. This has proven to be useful to many developers in the past, and hopefully will serve you well too.
Sorry we can’t be of more help here.