After the outbreak of strangenesses, Zhang Xiaomo's teacher discovered that the magnetic field control he was studying played a significant role. He altered his own body's magnetic field in his experiments, and could be considered one of the first exorcists.
Subsequently, a large number of people capable of controlling their internal magnetic fields, forming magnetic force, were discovered or unearthed. Then, the exorcist teams were established; while the founders weren't Zhang Xiaomo's parents, they were among the first of the veteran members.
Actually, Zhang Xiaomo's control over magnetic force was only above average, not the best. Now, nearly a year since the outbreak of strangenesses, some more bizarre or, rather, more powerful humans were being discovered and recruited by the exorcist teams.
For example, people like Yan Junze who possessed the Buddhist Exorcism Method, or those whose sensitivity to strangenesses was at its ultimate peak.