Why did police file NCR against Parvesh Verma and FIR against AAP MLA after 'slap' row?

Delhi Police registered a non-cognisable report (NCR) against Delhi minister Parvesh Verma and FIR against AAP MLA Jarnail Singh after Verma slapped a man. FIR against Singh was based on a PWD engineer's complaint alleging obstruction and intimidation of public servants, while the NCR against Verma was for "voluntarily causing hurt". Police need a magistrate's permission to investigate an NCR.