Could a "phantom" citation in WoS be a problem?
I believe that you have answered yourself in your question:


  And even if there were some situations where somebody uses WoS as a way to evaluate my work, being cited in one paper does not influence the total result too much.


Nobody expects databases to be perfect.  You are expected to do a reasonable job of self-curation, such that you are not, say, doubling your citation count by adding in many papers by other people.  Small percentage errors, however, will change nothing significant in any evaluation of you and your work.