It was because of a sudden surge of curiosity that Zachary, through Divine Sense, discovered that someone was actually watching him.
Observing the private discussion about how to 'bump into' him casually, Zachary first used his Divine Sense to assess their abilities.
From the conversation among the four of them, it was clear that Spider was the leader of the team. Through Spiritual Sense Scanning, Zachary determined that Spider had the physical quality of a junior Martial Artist.
It made sense, being the leader of a scamming team, it was unlikely that he would undergo strenuous training, yet obtaining a Cultivation Technique and nutritional supplements through certain channels shouldn't be difficult.
Spirit Dog was just an ordinary person. Although Zachary wasn't sure if he had started cultivating, the Divine Sense revealed that his physical fitness should be above average.