وَمِصْدَاقُهُ وُقُوعُ الْعِلْمِ مِنْ غَيْرِ شُبْهَةٍ
Its indication is the occurrence of knowledge without a remaining doubt.
The passage treats the attainment of certainty as a key mark of tawātur. This does not mean that anyone's intense personal confidence automatically counts as tawātur. Psychological conviction and properly grounded certainty are not interchangeable.
A distant city's existence may become known through a robust network of independent testimony and public dealings, even without personal travel. The epistemic force lies in the composite evidence, not in the confidence or eloquence of one speaker.