Let's go back a few weeks, when the hunt for Rosso was in full force, making it harder for him to exist in the city.
There were mystics, curse masters, and even spiritualists who rarely appeared in this world, who came and tried to look for him.
But no traces of his were detected, none at all.
To the world, he appeared dead, which no one really believed. Such a powerful being can't die so easily.
Even if he faces a strong foe, a being of Rosso's level would obviously leave some traces. None of which were found around Rudrain or anywhere close to Rudrain for that matter.
Which meant that the opponent they were looking for had greater anti-tracking methods than they could ever fathom.