The key difference between assurance services and consulting services is that other employees in the organization can provide consulting services, but only an internal audit activity can provide assurance services.
This distinction is important because assurance services require a level of independence and adherence to specific standards that are unique to the internal audit profession. References: IIA definitions and standards for assurance and consulting services, which delineate the roles and limitations of these services within internal audit practices.

The scenario described involves a violation of the principle of confidentiality as defined in The IIA's Code of Ethics. The internal auditor misused information obtained during the course of an audit (salary data of colleagues) for personal gain (requesting a salary raise). This breaches the ethical principle of confidentiality, which mandates that auditors respect the value and ownership of information they receive and do not disclose information without appropriate authority unless there is a legal or professional obligation to do so.References:
The IIA's Code of Ethics on Confidentiality.