Seth had to be certain that what Lexi had told him was not the truth, or else he wouldn't be able to rest in peace until he punished whoever tried to hurt her.
He activated his Soul Sense while going towards the place Chun Meiyi went to collect the herbs at full speed. In less than five minutes he was already standing on that particular area.
In his slightly uncontrollable state, Seth's Soul Sense expanded to the maximum and he was able to find traces of soldiers dressed in robes of the Wu Martial Kingdom, patrolling some points inside the forest.
His first reaction was to actually stop and quickly contemplate everything. Seth didn't think Lexi's theory would be so accurate. Meiyi's healed wounds and the condition she was in; soldiers patrolling the area she went to collect herbs and the coincidental time and place that these things happened.