There are 2 columns that can be used in Insight for reporting the type of applicant.
The first is Applicant type from Recruitment Applicant master. This will report on the applicants current status which include internal/external. If an applicant is External and they are hired after completing recruitment then their status will change to Internal
The second is Application type which reports the applicants status of internal/external for that specific application. So even if an applicant was hired as part of recruitment, this status does not change from External for a specific competition. It will change once they apply for a job internally however.