There are 2 rules relating to Candidate Ownership when processing details from Job Boards.
Parsing Job Board Search Candidates
When parsing Candidates from the results of a Job Board Search, the user actioning the download will become the Candidate's Owner, not the Job Owner.
Job Board Applicants
When receiving Job Board Applications, Tracker will first look to see if there is a "Main Contact" in the Publish section of the Job record and if so, assume ownership to that user. If this is not set, then the Job Owner will be used for the Candidate Ownership.