When accessing the Scheduling > Exam Clashes page, this report will show you clashes for both your external and your In-house exams together. You can see more information here: Resolving exam clashes
It isn't possible to filter the results to look at only the clashes for your In-house exams for example.
You can change the date range using the filters to when the In-house exams took place. As In-house exams usually happen at a different point in the year, this should help remove the external exams from the list.