It is not unusial a rejected manuscript is being resubmitted to another journal. If the manuscript is eventually published with unaltered title in Journal 2, in a reviewer Publons' profile, the rejected paper is displayed as if it was published in Journal 1.
Andrew here from Publons, thanks for your message. Since you reviewed the paper for Journal 1, that review should be displayed as being performed for Journal 1. If your review is signed/published and you go to the publication detail page it should show that the paper was published in Journal 2 but that your review was for Journal 1. If you have a particular example which contradicts this please let me know.